The first generation of the CBU-55 was used during the Vietnam War, but only in a test mode by US forces. In 1971, a team from the Air Force Weapons Center at Eglin Air Force Base brought test versions of the CBU-55 to Southeast Asia for testing on two lower speed attack aircraft, the A-37 and the A-1. In late 1971, the team worked with the 604th Special Operations Squadron A-37 pilots at Bien Hoa Air Base to fly a handful of combat test missions. In December of that year, that same team came to Nahkon Phanom Royal Thai Air Base (NKP) to do the same tests with the 1st Special Operation Squadron, flying the A-1. On Dec 2nd, 5th, and 8th, three two ship A-1 sorties were flown, carrying four each of the CBU-55. The NKP test project officer and flight lead for these three missions, Capt. Randy Jayne, helped the Eglin team write up the test results, which were overall not positive. The unusual deployment sequence for the three propane canisters, and the fact that they fell under small parachutes highly susceptible to significant wind drift, made deliver accuracy and aircraft survivability (when releasing low enough to minimize that wind drift) questionable. Also, the very high drag characteristics of the CBU-55 canister, with its flat back end, severely limited the A-1's ability to carry other bombs, rockets, and CBU, a further negative issue. In February/March 1972 US Navy Light Attack Squadron 4 (VAL-4) based at Can Tho delivered several sorties with the OV-10 Bronco, in support of US Army and ARVN joint operations north of the Mekong River. The ordnance was considered experimental, and teams of pathologists were flown to the drop sites to examine weapon effects on enemy remains.