With the North Vietnamese invasion, the drones were launched at an average rate of nearly two per day. Some days saw as many as five launches, with nine drone missions flown over a three-day period. This was far higher than during Rolling Thunder. The 147SC drones covered areas that were denied to manned reconnaissance aircraft as too dangerous. This included not only Hanoi and Haiphong, but all of North Vietnam and even occupied areas of South Vietnam.[284]
As the bombing continued during the summer and fall, a new version of the 147SC was introduced. The SC/TV was first flown in June 1972. As the name suggests, this was a standard SC fitted with a television camera. The images were transmitted to a controller aboard the DC-130. He would then guide the drone over the target. This made it possible to cover exactly that part of a target needed. On one SC/TV mission, eight out of nine targets were covered and three bonus targets were also spotted, this despite visibility of down to two miles.[285]
The following month the last of the 147N family began combat operations. The 147NC had an unusual history. It originally was built for dropping radar-jamming chaff and had been operated by the tactical air command for several years. It had not, however, been sent to Vietnam. The chaff was carried in two external pods. It was realized the pods could also carry propaganda leaflets over North Vietnam.
Between July and December 1972, twenty-eight missions were flown by the 147NC drones. The biggest problem faced by the drones was predicting the wind over the target at the time of the drop. The leaflets would drift on the wind after release. Several missions were ineffective because the winds carried the leaflets away from the target. The project's official name was "Litterbug." The working troops called the drones "bullshit bombers."
In September 1972, a final series of four 147H missions was flown. The cameras were replaced with ELINT equipment. As with the United Effort missions of 1965-66, the purpose of this special project, called "Compass Cookie," was to gain radar and fuze data on the SA-2. A number of new versions had been introduced since 1966, and the mission would provide an update. The September 28 mission was fired on by three SA-2s but transmitted the data before being destroyed.[286]
By the fall, a peace agreement seemed complete. Nixon ordered a bombing halt above the twentieth parallel on October 24, while Kissinger declared, "Peace is at hand." The final details proved elusive, however. The North Vietnamese reopened several issues and finally broke off talks on December 13. Five days later, B-52s began hitting targets in Hanoi and Haiphong in tlie most intense air campaign in history. Linebacker ll became known as the Eleven-Day War. The B-52s took heavy losses, but devastated airfields, factories, railyards, warehouses, and SAM sites.
Linebacker II saw the drone's heaviest use of the entire war. Between December 20, 1972, and January 19, 1973, over 100 missions were flown.
Two-thirds of these were bomb damage assessment (BDA) missions in support of the B-52 strikes. The photos showed the targets were turned into cratered moonscapes. The drones also photographed POW camps in the Hanoi area. Throughout the war, POWs had seen or heard the drones many times. During the 1968-72 bombing halt, they were one of the few things sustaining the prisoners' morale.
The final B-52 strikes were flown on December 29, 1972. Following a New Year's halt, bombing was restricted to below the twentieth parallel. On January 15, 1973, agreement was reached and all bombing of North Vietnam stopped. It was announced that reconnaissance flights would continue over North Vietnam. They would be conducted by SR-71s and low-altitude drones. One Pentagon official said, "The use of pilotless drones is no change and is one method we have used whenever bombing missions over North Vietnam have been halted." It was as close to an official acknowledgment as had been made. The final flight before the cease-fire went into effect was a 147SC/TV, dubbed "The Last Picture Show." A total of 570 drone missions had been launched in 1972. Of this, 466 were SC drones (52 were lost), while the 147TEs amounted to a mere 69 flights.[287]
The cease-fire agreement was signed on January 27, 1973. The drones were placed on a "hold/standby" status. This lasted only five days. Operations resumed with a pair of flights on February 5. The following day, the first of a series of SC/TV missions was launched. Policing the cease-fire was nearly as demanding as Linebacker had been: 444 drone missions were launched in 1973.
The year saw the debut of the final two members of the 147S family, the 147SD and SDL. The SD was designed with an improved navigation system with an accuracy of 1.1 miles per 100 miles. (The SC's accuracy was 3 percent.) The SD also had an improved radar altimeter, a new cooling system to cope with low-altitude flight in hot tropical weather, and external tanks to extend the range. The first 147SD mission was flown in June.
The other was the SDL. This was a 147SD equipped with a Loran radio-navigation system, which provided even greater accuracy. The first two missions had actually been flown in August 1972, but both were lost. The cause was traced to interference from the navigation system. Normally, the drone would bank up to a maximum angle. Once at this point, the guidance system would not accept any further bank commands. It was found that the Loran was generating an override signal to the roll control; the bank angle increased and the drone went out of control.
Survivability of these last-generation drones was also phenomenal. By November of 1973 there had been 100 launches without a loss. The 147SC drones were designed for an average lifetime of two and a half missions each. They would far surpass this. The record holder was "Tom Cat," with 68 missions, each covering an average of twelve targets. The runners-up were "Budweiser" (63 missions), "Ryan's Daughter" (52 missions), and "Baby Buck" (46 missions). A 147SC/TV flew 42 missions, an SD made 39, while an SDL made 36 missions.
The final eighteen months of drone operations — between 1974 and early June 1975—saw a total of 518 flights. From the start, it was discovered that the North Vietnamese were violating the peace agreement. Troops, tanks, and SAMs poured into the South. The United States, its spirit broken by the war and increasingly obsessed with the Watergate scandal, was both unwilling and unable to do more than issue feeble protests.
By early 1975, the North Vietnamese began their final offensive. The South Vietnamese army was driven back, while the U.S. Congress cut off all aid. By late April, Saigon was surrounded. The United States began an evacuation, and South Vietnamese aircraft and helicopters began to flee.
The final 147S-series mission was flown on April 30, 1975—the day Saigon fell.
With the fall of Saigon, the 147SC and SD drones were put into storage.
The 147TF drones continued a little longer. The final flight was made on June 2, 1975. Then they, too, were stored. Although some in Congress objected to the loss of so valuable a capability, the decision stood.
The story of the Model 147 drones was an amazing chapter in the history of U.S. Black aircraft. Using the existing Firebee drone gave it flexibility, while new versions were developed on a short-time scale at low cost. The result was a reconnaissance capability that was unmatched by manned aircraft. In all, 3,435 drone missions were flown against Communist China, North Vietnam, and North Korea. Of these, 1,651 were by 147SC drones. A total of about 1,000 147SC drones were built, in nineteen different versions.
285
Ibid., 199. The 147SC/TV did have a major problem — a tendency to just fall out of the sky. The problem was traced to the fin-shaped antenna that transmitted the television signals to the DC-130. It was found that the fin caused the drone to become directionally unstable. Once it was replaced with a flush antenna, the problem disappeared.
287
Ibid., 198–200. The 147 drones live on in China. In the 1970s, photos were published of a Chinese copy of reconnaissance drones very similar to the 147G/H high-altitude drones. The launch aircraft was a Tu-4 (a Soviet-built copy of the B-29) modified with turboprop engines.