Operation Ivory Coast

Operation Ivory Coast was a failed rescue mission conducted in North Vietnam during the Vietnam War by United States Special Operations Forces and other elements of the U.S. military.

On 21 November 1970, a joint United States Air Force/United States Army force commanded by Air Force Brigadier General LeRoy J. Manor and Army Colonel Arthur D. "Bull" Simons landed 56 U.S. Army Special Forces soldiers by helicopter in the Sơn Tây prisoner-of-war camp located only 23 mi west of Hanoi, North Vietnam. The mission's objective was the recovery of 61 American prisoners of war thought to be held at the camp, situated in an area where 12,000 North Vietnamese troops were stationed within 5 mi. The mission failed when it was found during the raid that all the prisoners had been previously moved to another camp.

The specially selected raiders extensively trained and rehearsed the operation at Eglin Air Force Base, Florida, while planning and intelligence gathering continued from 25 May to 20 November 1970. Despite the absence of prisoners, the raid was executed with a high degree of success, incurring only two minor casualties and the loss of two aircraft, one of which had been part of the plan from the start. Criticism of intelligence failures to determine that the camp was empty of U.S. POWs, both public and within the administration of President Richard M. Nixon, led to a major reorganization of the United States intelligence community a year later.

Polar Circle
The concept of a rescue mission inside North Vietnam began on 9 May 1970. An Air Force intelligence unit concluded through analysis of aerial photography that a compound near Sơn Tây, suspected since late 1968 of being a prisoner of war camp, contained 55 American POWs and that at least six were in urgent need of rescue. On 25 May the unit met in the Pentagon with BG Donald Blackburn, Special Assistant for Counterinsurgency and Special Activities (SACSA), to report their findings. Blackburn was responsible directly to the Chairman of the Joint Chiefs of Staff and had also been the first commander of the covert Studies and Observation Group in Vietnam.

Blackburn immediately met with General Earle G. Wheeler, the JCS Chairman, to recommend a rescue of all the POWs at Son Tây. To study the feasibility of a raid, Wheeler authorized a 15-member planning group under the codename Polar Circle that convened on June 10. One of its members was an officer who would actually participate in the raid as a rescue helicopter pilot. The study group, after a review of all available intelligence, concluded that Sơn Tây contained 61 POWs.

When Blackburn's recommendation that he lead the mission himself was turned down, he asked COL Arthur D. Simons on 13 July to command the Army's personnel. Eglin Air Force Base was selected as the joint training site for the prospective force. Personnel selection proceeded over the objections of the Marine Corps, which was excluded from participation, but selection and planning was performed by Special Operations "operators", not by the JCS, to avoid service parochialism, resulting in a force chosen for mission needs, highlighting combat experience in Southeast Asia and operational specialty skills, and not rank or branch of service.

Ivory Coast
The second phase, Operation Ivory Coast, began on 8 August 1970, when Admiral Thomas H. Moorer, the new J.C.S. Chairman, designated Manor as commander and Simons as deputy commander of the mission task force. Ivory Coast was the organization, planning, training, and deployment phase of the operation. Manor set up an Air Force training facility at Eglin's Duke Field and brought together a 27-member planning staff that included 11 from the prior feasibility study.

Simons recruited 103 personnel from interviews of 500 volunteers, most Special Forces personnel of the 6th and 7th Special Forces Groups at Fort Bragg, North Carolina. USAF planners selected key Air Force commanders, who then picked personnel for their crews. Helicopter and A-1 Skyraider crews were put together from instructors at Eglin and personnel returned from Southeast Asia. Two crews for C-130E(I) Combat Talons were assembled from squadrons in Germany and North Carolina. All were then asked to volunteer for a temporary duty assignment without additional pay and without being told the nature of the mission. 103 Army and 116 Air Force personnel were selected for the project, including ground force members, aircrewmen, support members, and planners. The 219-man task force planned, trained, and operated under the title of the "Joint Contingency Task Group" (JCTG).

The planning staff set up parameters for a nighttime raid, the key points of which were clear weather and a quarter moon at 35 degrees above the horizon for optimum visibility during low-level flight. From these parameters, two mission "windows" were identified, 18–25 October and 18–25 November. Training proceeded at Eglin using a replica of the prison compound for rehearsals and a $60,000 five-foot-by-five-foot scale table model (codenamed "Barbara") for familiarization.

Air Force crews flew 1,054 hours in southern Alabama, Georgia, and Florida conducting "dissimilar (aircraft) formation" training with both UH-1H and HH-3E helicopters at night and at low-level (a flight profile for which procedures had to be innovated by the two selected crews), and gaining expertise in navigation training using forward looking infrared (FLIR), which, until Ivory Coast, had not been part of the Combat Talon's electronics suite. A vee formation in which the slower helicopters drafted in echelon slightly above and behind each wing of the Combat Talon escort aircraft was chosen and refined for the mission to give the helicopters the speed necessary to keep pace with the Talons flying just above their stall speeds.

Special Forces training began on 9 September, advancing to night training on 17 September and joint training with air crews on 28 September that included six rehearsals a day, three of them under night conditions. By 6 October, 170 practice sessions of all or partial phases of the mission were performed on the mockup by the Special Forces troopers, many with live fire. On that date, the first full-scale dress rehearsal, using a UH-1H as the assault helicopter, was conducted at night and included a 5.5-hour, 687 mi flight of all aircraft, replicating the timing, speeds, altitudes, and turns in the mission plan. The rehearsal spelled the end of the option to use the UH-1 when its small passenger compartment resulted in leg cramps to the Special Forces troopers that completely disrupted the timing of their assault, more than offsetting the UH-1's only advantage (smaller rotor radius) over the larger HH-3. Two further full night rehearsals and a total of 31 practice landings by the HH-3E in the mockup's courtyard confirmed the choice.

On 24 September, Manor recommended approval of the October window to US Secretary of Defense Melvin Laird, with 21 October as the primary execution date. However, at a White House briefing on 8 October with National Security Advisor Henry Kissinger and General Alexander M. Haig, Kissinger delayed the mission to the November window because President Nixon was not in Washington and could not be briefed in time for approval of the October window. This delay, while posing a risk of compromising the secrecy of the mission, had the benefits of additional training, acquisition of night-vision equipment, and further reconnaissance of the prison.

Manor and Simons met with the commander of Task Force 77, Vice Admiral Frederic A. Bardshar, aboard his flagship USS America on 5 November to arrange for a diversionary mission to be flown by naval aircraft. Because of policy restrictions of the bombing halt then in place, the naval aircraft would not carry ordnance except for a few planes tasked for Search and Rescue.

Between 10 and 18 November, the JCTG moved to its staging base at Takhli Royal Thai Air Force Base, Thailand. The Combat Talons, using the call signs Daw 43 and Thumb 66 in the guise of being a part of Project Heavy Chain, left Eglin on 10 November, flew to Norton Air Force Base, California, and then routed through Hickam Air Force Base, Hawaii and Kadena Air Base, Okinawa, arriving in Takhli on 14 November. The next day, four C-141 Starlifters departed one per day (to avoid the appearance of a major operation in progress), carrying the Army contingent of the JCTG, its equipment, and the UH-1 helicopter from Eglin to Thailand. The Special Forces personnel arrived in Thailand at 03:00 local time 18 November and later that date President Nixon approved execution of the mission, setting in motion the final phase, Operation Kingpin.

After overcoming in-theater friction with the 1st Weather Group at Tan Son Nhut Air Base, Vietnam, planners began watching the weather during the week before the projected target date. On 18 November, Typhoon Patsy struck the Philippines and headed west towards Hanoi. Weather forecasts indicated that Patsy would cause bad weather over the Gulf of Tonkin on 21 November, preventing carrier support operations, and converging with a cold front coming out of southern China, would cause poor conditions over North Vietnam for the remainder of the window. The presence of the cold front, however, indicated that conditions in the objective area on 20 November would be good and possibly acceptable over Laos for navigation of the low-level penetration flights. A reconnaissance flight on the afternoon of 20 November by an RF-4C Phantom carrying a weather specialist confirmed the forecast. Manor decided to advance the mission date by 24 hours rather than delay it by five days.

Manor issued the formal launch order at 15:56 local time 20 November, while the raiding force was in the final stages of crew rest, and brought together the entire ground contingent for a short briefing regarding the objective and launch times. Following the briefing, Manor and his staff flew by T-39 Sabreliner to Da Nang, where they would monitor the mission from the USAF Tactical Air Control Center, North Sector (TACC/NS) atop Monkey Mountain. Three theater lift C-130s previously staged at U-Tapao Royal Thai Navy Airfield arrived at Takhli to transport the Army contingent and helicopter crews to Udorn RTAFB and the A-1 pilots to Nakhon Phanom.

Special Forces
The fifty-six Special Forces troopers selected to conduct the raid were flown on the evening of 20 November by C-130 from Takhli to their helicopter staging base at Udorn RTAFB. The Special Forces were organized into three platoons: a 14-man assault group, codenamed Blueboy, which would crash-land within the prison compound; a 22-man support group, Greenleaf, which would provide immediate support for the assault team, and a 20-man security group, Redwine, to protect the prison area from NVA reaction forces and provide backup support if needed for either of the other two groups. Simons (using the call sign Axle) accompanied the Greenleaf group, while the ground force commander, LTC Elliott P. "Bud" Sydnor, Jr. (Wildroot), was with the Redwine group.

The 56 raiders were heavily armed, carrying a total of 51 personal sidearms, 48 CAR-15 carbines, two M16 rifles, four M79 grenade launchers, two shotguns, and four M60 machine guns. They carried 15 Claymore mines, 11 demolition charges, and 213 hand grenades and were equipped with a plethora of wire cutters, bolt cutters, axes, chainsaws, crowbars, ropes, bullhorns, lights, and other equipment (much of it acquired from commercial retail sources) to execute the mission. The ground force was also equipped for voice communications with 58 UHF-AM and 34 VHF-FM radios, including a survival radio for each individual soldier.

Aviation support


116 aircraft (59 Navy and 57 Air Force) participated in the operation, with 28 aircraft (crewed by 92 airmen) assigned direct roles in the target area. Two C-130E(I) Combat Talons, modified with the temporary addition of FLIR sets, were assigned to navigate the mission. One was to lead the helicopter "assault formation" (Cherry 01) and the second to escort the A-1 "strike formation" (Cherry 02). Because of the variances in cruising speeds between the helicopters and fixed-wing aircraft, the forces flew separate routes, with the faster strike formation trailing the helicopter formation by several minutes and zig-zagging across its route. Each Combat Talon crew cross-trained to assume the role of the other, but the assault formation was required to have a navigation leader with four fully functioning engines all the way to the objective.

The 28 aircraft with direct roles were:

Penetration into North Vietnam
Beginning at 22:00 20 November 1970, aircraft began leaving five bases in Thailand and one in South Vietnam. Cherry 02, the Combat Talon escort for the A-1 strike formation, took off from Takhli at 22:25. Cherry 01, scheduled to take off a half hour later, had difficulty starting an engine and took off 23 minutes late at 23:18. Cherry 01 adjusted its flight plan and made up the time lost at engine start. At 23:07, the HC-130P aerial refuelers (call signs Lime 01 and Lime 02) took off from Udorn, followed by the helicopters ten minutes later. Shortly after midnight, the A-1 Skyraiders lifted off four minutes early from Nakhon Phanom Royal Thai Air Force Base under clandestine, blacked-out conditions. The helicopters encountered thick clouds over northern Laos at their refueling altitude and climbed to 7000 ft AGL (Above Ground Level) to refuel from Lime 01 on the flight plan's fourth leg. Lime 01 then led them to the next checkpoint for hand-off to Cherry 01 at 01:16.

The formations flew roughly parallel tracks that crossed Laos to the west of the Plain of Jars before turning northeastward. Both formations flew twelve planned legs. The flight path was a corridor 6 mi wide, the width required for safe terrain clearance in the event of formation breakup or the loss of drafting position by a helicopter. The Combat Talon navigators had the task of keeping the formations on the center line of the corridor. Pilots of both formations required a flight path of descending legs, maintaining an altitude of 1000 ft above ground level in the mountain valleys, because the HH-3E had difficulties in climbing while in formation. The Combat Talon C-130s experienced sluggish flight controls at the required airspeeds, and the A-1s were hampered by their heavy ordnance loads.

The slow speeds necessary for the formations, 105 kn for the helicopters and 145 kn for the A-1s, degraded nearly all modes of the Combat Talon's AN/APQ-115 TF/TA navigational radars. The Terrain Following mode computed changes in altitude only to a programmed minimum airspeed of 160 kn, well outside the parameters of the mission. The Terrain Avoidance mode (adapted from the AN/APQ-99 terrain avoidance radar of the RF-4C photo reconnaissance aircraft) was distorted by the nose-high attitude dictated by the slow speeds and would no longer display hazardous terrain directly in front of or below the Combat Talon's flight path. The Doppler radar (used to calculate wind drift and ground speed) often had to use information in its computer's memory because of processing lapses. While the ground-mapping radar (correlating landmarks shown on maps to radar returns) was not affected, the jungle terrain did not provide easily identifiable points. All of these handicaps were overcome with the external pod installation of FLIR, which readily identified the rivers and lakes used as turning points.

The assault formation approached from the southwest using the clutter returns of the mountains to mask them from radar detection, while U.S. Navy aircraft launched at 01:00 21 November from the aircraft carriers USS Oriskany and USS Ranger in the largest carrier night operation of the Vietnam War. Starting at 01:52, twenty A-7 Corsairs and A-6 Intruders, flying in pairs at stepped-up altitudes to deconflict their flight paths, entered North Vietnamese airspace on three tracks, dropping flares to simulate an attack. The last track also dropped chaff to mimic the mining of Haiphong harbor. Over the Gulf of Tonkin, twenty-four other aircraft in thirteen orbits provided support and protection. The operation prompted a frantic air defense reaction at 02:17 that provided a highly effective diversion for the raiders and completely saturated the North Vietnamese air defense system.

Both Air Force formations, over a period of thirteen minutes, were unavoidably but separately exposed for several minutes each to an early warning radar located at Na San, North Vietnam, 30 mi to the north, because the flight tracks had to be routed around uncharted mountains. Neither formation was detected, possibly because of the diversion. The rescue forces entered the Red River valley at 500 ft AGL to find conditions clear and visibility excellent. The helicopter formation reached its Initial Point (20 kilometers—12 minutes flying time—from Son Tây) with the A-1 strike formation two minutes behind, as planned. The HH-3E assault team helicopter had flown formation just behind and above the left wingtip of Cherry 01, drafting on the leader to gain the additional airspeed needed to bring its cruise airspeed safely above the stalling speed of the Combat Talon. Cherry 01 and the two HH-53s designated for prisoner pickup accelerated to climb to 1500 ft AGL, while the four assault helicopters broke formation and descended to 200 ft in single file, timed to land forty-five seconds apart.

Combat assault
At 02:18 Cherry 01 transmitted the execute command "Alpha, Alpha, Alpha" to all aircraft as it overflew the prison and deployed four illumination flares, then performed a hard-turning descent to 500 ft to drop two battle simulators south and southeast of Sơn Tây. After Apple 03 made its strafing pass with side-firing miniguns on the prison's guard towers, Cherry 01 successfully dropped one of two planned napalm ground markers as a point of reference for the A-1s, then departed the objective area to a holding point over Laos where it would provide UHF direction-finding steers for the departing aircraft.

The assault helicopters in single file encountered winds that caused them to break formation 150 yd to the right of their intended track. The pilots of Apple 03, the gunship helicopter preceding the others, observed a compound nearly identical to the prison camp in size and layout (previously labeled a "secondary school" by intelligence sources) and steered toward it, followed by the assault lift force. However, they recognized their error when they saw the river next to the actual location and corrected their flight path. Banana, the HH-3E carrying the Blueboy assault team, descended on the wrong location and observed that the expected courtyard was much smaller than required and that the expected treeline enclosed the compound rather than crossing through it. By that time, Blueboy (as previously rehearsed) was firing its weapons from all openings in the helicopter. Banana's pilots also recognized the error, applied power, and quickly veered north to the actual target.

Despite the error, and trees taller than briefed that forced a steeper descent than rehearsed, the assault team crash-landed into the courtyard of Sơn Tây prison at 02:19 with all weapons firing. Although one raider, acting as a door gunner, was thrown from the aircraft, the only casualty was the helicopter's flight engineer, whose ankle was fractured by a dislodged fire extinguisher. Army Captain Richard J. Meadows used a bullhorn to announce their presence to the expected POWs, while the team dispersed in four elements on a rapid and violent assault of the prison, killing guards and methodically searching the five prisoner blocks cell by cell.

Also at 02:19, Apple 01 (after its pilots saw Banana fire on the first location) landed the Greenleaf support group outside the south side of the secondary school, thinking it to be the target prison compound. Unaware that it was 400 meters from the objective, it lifted off to relocate to its holding area. The "secondary school" was actually a barracks for troops that, alerted by Banana's aborted assault, opened fire on Greenleaf as two of its elements assaulted the compound. The support group attacked the location with small arms and hand grenades in an eight-minute firefight, after which Simons estimated that 100 to 200 hostile soldiers had been killed. Two A-1s supported Greenleaf with an air strike using white phosphorus bombs on a wooden footbridge east of the area. Apple 01 returned at 02:23, and by 02:28, the support group had disengaged under fire and reboarded the helicopter for the short movement to the correct landing area.

The pilot of Apple 02 observed the errors in navigation by the helicopters in front of him and made a hard turn towards the prison. He also observed Apple 01 unload at the secondary school and initiated Plan Green, the contingency plan for the loss or absence of Greenleaf. The Redwine security group, including ground force commander Sydnor, landed at 02:20 outside Sơn Tây prison and immediately executed the previously rehearsed contingency plan. In the meantime, Cherry 02 arrived with the A-1 force, dropped two more napalm ground markers, and created other diversions to disguise the target area by dropping MK-6 log flares and battle simulators at road intersections that North Vietnamese reaction forces might be expected to use. Cherry 02 then orbited in the area just west of the Black River acting as on-call support for the ground teams, jamming North Vietnamese radio communications, and providing a secure radio link to the mission command post in Da Nang.

After a thorough search that included a second sweep ordered by Meadows, Blueboy's three teams found that the prison held no POWs. Meadows transmitted the code phrase "Negative Items" to the command group. Pathfinders clearing the extraction LZ blew up an electrical tower that blacked out the entire west side of Sơn Tây including the prison area. At 02:29, Sydnor ordered the A-1s to attack the vehicle bridge over the Song Con leading into the area and, three minutes later, called for extraction by the HH-53s idling on the ground in a holding area a mile away. Before the first helicopter arrived, a truck convoy approached the prison from the south, but was stopped by two Redwine security teams that each fired an M72 light antitank weapon into the lead vehicle.

At 02:28, Cherry 02's electronic warfare operator noted that Fan Song fire control radars for North Vietnamese surface to air missile (SAM) sites had gone active. SAM launches at the F-105 Wild Weasel force began at 02:35, with at least 36 missiles fired at the rescue forces. One F-105 was briefly enveloped in burning fuel by a near-miss at 02:40 and returned to base. Its replacement was severely damaged six minutes later by another SAM. Twenty other SAMs fired at Navy aircraft all missed. Two MiG-21 interceptors on alert duty at Phúc Yên Air Base were never given permission to launch, despite several requests to do so.

Extraction of the raiders
The HH-53s returned singly to the extraction landing zone amidst the SAM barrage, flying well below the minimum effective level of the missiles, and Apple 01 landed first at 02:37. It lifted off with its passengers at 02:40, followed a minute later by the landing of Apple 02, which departed at 02:45. Apple 03, the last aircraft out, was cleared to leave its holding area at 02:48. The raid had been executed in only 27 minutes, well within the planned 30-minute optimum time. Although at first it was feared one raider had been left behind, all the troopers were accounted for. One Redwine trooper had been wounded in the leg and was the only casualty to hostile fire on the raid.

Shortly after its departure, Apple 03 mistook a support fighter for a MiG and called a warning, and although one of the Combat Apple KC-135s supporting the mission issued information that no MiGs had taken off, the entire force descended to treetop altitude. Apple 04 reported that a MiG had fired an air-to-air missile at it that missed, but this was later found to have been aerial rockets fired into a hillside by one of the A-1 escorts to increase its maneuverability after the erroneous MiG call.

The assault formation was out of North Vietnam by 03:15 and landed back at Udorn at 04:28, five hours after launch. The crew of the damaged F-105 was compelled to eject over Laos thirty minutes after being hit when it flamed out from lack of fuel in sight of its tanker. Lime 01, refueling at Udorn, took off using the call sign King 21 to coordinate the Search and Rescue (SAR) effort, while Lime 02 refueled Apple 04 and Apple 05 to extend their flight time. Supported by a C-123 Candlestick flare aircraft diverted from its station on another mission, a SAR force was launched, and when its "Sandy" A-1s arrived from Nakhon Phanom to cover the pickups, Apple 04 and Apple 05 each recovered one of the downed airmen at first light after three hours on the ground.

Intelligence controversy


The mission was deemed a "tactical success" because of its execution, but clearly involved an "intelligence failure". The 65 prisoners at Sơn Tây had been moved on 14 July because its wells had been contaminated by flooding, or possibly due to the threat of further inundation, to a camp 15 mi closer to Hanoi that the POWs dubbed "Camp Faith". Although relatively near Sơn Tây, the risk of disastrous consequences from lack of reconnaissance, planning, and rehearsing precluded a switch of targets at the last minute. A mission with Camp Faith as the objective required a lengthy delay for a new window of acceptable conditions, which increased the chance of security compromise and further withheld personnel and equipment from their parent commands. New reports of increasing numbers of deaths among POWs argued strongly against such a delay. The raid went as planned in the event the renewed activity at Sơn Tây noted in aerial reconnaissance photos taken November 13 involved POWs.

Although the mission objective involved an intelligence failure, the gathering of accurate intelligence for the operation, in both quality and quantity, was remarkably successful. The failure lay in "compartmentalization" of the information and isolation of the JTCG from "the normal intelligence flow". As a planner and participant stated in his history of the operation: "The raid was allowed to take place because those who had the correct intelligence information were not aware that someone was contemplating a POW rescue."

Further, by the time intelligence regarding the moving of the prisoners was received, prompting the Defense Intelligence Agency to do an intensive overnight re-analysis of all of its data, the day of the operation had already arrived as a result of the 24-hour advancement of the operation due to Typhoon Patsy and the 12-hour time difference with Southeast Asia. When a final meeting with Defense Secretary Melvin Laird took place at 05:00 (Washington, D.C., time) to determine if the mission should proceed, its launch was less than five hours away. There was no consensus on the reliability of the data, and Blackburn was strongly predisposed to go ahead. One military analyst observed that as a result, the highest-level decision makers succumbed to the phenomenon of "groupthink".

Recognition of participants
For their actions, members of the task force received six Distinguished Service Crosses, five Air Force Crosses, and at least 85 Silver Stars, including all 50 members of the ground force who did not receive the DSC. Manor received the Distinguished Service Medal.

The successful demonstrations of joint operating capability in Ivory Coast and Kingpin were, in part, a model for the creation of a joint United States Special Operations Command in 1987.

Sơn Tây raider HH-53 68-10357 (Apple 01) was subsequently converted to MH-53M Pave Low standard, served in Bosnia and Iraq and was finally retired in 2008 after 38 years of service. It is now on display in the Cold War Gallery of the National Museum of the United States Air Force in Dayton, Ohio.

Combat Talon 64-0523 (Cherry 01) was redesignated "MC-130E" in 1977 and assigned to the 7th Special Operations Squadron in Germany. In January 1994 it left operational service and became a weapons system trainer with the 58th Special Operations Wing at Kirtland AFB, New Mexico, and then was transferred to the 711th Special Operations Squadron of the Air Force Reserve Command in March 1997. Retired in 2012 after 48 years of service, Cherry 01 was placed on permanent display as a gate guard at Cannon Air Force Base, New Mexico.

Impact of the raid
Criticism of the raid, particularly in the news media and by political opponents of the Vietnam War and the Nixon Administration, was widespread and of long duration. Not only was the failure denounced as the result of poor or outdated intelligence, but charges were made that the operation caused increased mistreatment of the prisoners.

However, as a result of the raid, the North Vietnamese consolidated their POW camps to central prison complexes. An area of the infamous "Hanoi Hilton" formerly housing civilian and South Vietnamese prisoners became "Camp Unity", a block of large communal areas housing 50 POWs each. After their repatriation, many POWs said that being in close contact with other Americans lifted their morale, as did knowledge of the rescue attempt. Some POWs said that food, medical care, and even seemingly basic things like mail delivery vastly improved after the raid.

The Defense Department conducted an investigation into a possible breach of security as the reason behind the movement of the prisoners and concluded that none occurred. The intensity of the criticism, and leaks of information including reports of the operation, caused the Nixon Administration to reorganize both the military communications network and the government's intelligence apparatus.