From the Planes You’ve (Probably) Never Heard Of Department of Aviation History, this is the Grumman AF Guardian.
The hunter-killer team: AF-2W in the foreground with ventral radome, and AF-2S in the background. (US Navy photo)
The submarine gained prominence as a serious menace to shipping during WWI. The Germans in particular operated a fleet of U-boats that strangled trade to England and her allies, and harassed shipping of all kinds. To fight the scourge of the U-boat, the combatants started to employ aircraft for the first time, but their role was mostly limited to patrol, forcing the submarines to submerge and hide to avoid attack from surface ships. During WWII, advances were made in airborne radar and the use of the magnetic anomaly detector (MAD) to locate submarines, and the US even produced a homing torpedo that could be dropped from an aircraft. Thirty-seven submarines were sunk in this way. These new aerial countermeasures were relatively successful, but the radars and weapons were adapted to existing aircraft. The purpose-built antisubmarine warfare (ASW) aircraft had yet to be created. That all changed in 1945, but not with just one aircraft.
AF-2S restored in the livery of Antisubmarine Squadron VS-25. This aircraft is now on display at the National Naval Aviation Museum. (US Navy photo)
The problem faced by aircraft designers in late WWII was that the equipment and ordnance necessary for finding and destroying submarines added up to quite a payload. Any aircraft big enough to carry the load by itself would have to be quite large, and the first attempt at an all-in-one ASW aircraft was the twin-engine Grumman XTB2F. By the time the project reached mockup, it was clear that the airplane would be too large to operate from Essex-class carriers and the project was abandoned. Next, Grumman considered a modified F7F Tigercat called the XTSF, but that was also deemed too big even for the larger Midway-class carriers. Then Grumman engineers came up with a breakthough idea: if one aircraft was too large, why not make two aircraft and share the load? The first aircraft would act as the hunter, equipped with a radar, while the second aircraft would act as the killer, armed with rockets, bombs, torpedoes or depth charges. Destroying submarines would now be a team effort.
The second U.S. Navy Grumman AF-2W Guardian, BuNo 123091 (US Navy photo)
Grumman and the Navy settled on the XTB3F, an aircraft that began as an internal project by Grumman to produce a torpedo bomber. The hunter aircraft, designated the AF-2W, was unarmed, carried a crew of three and was equipped with a ventral radome housing an APS-20 radar and other electronic countermeasures. The killer aircraft, designated AF-2S, had a crew of four and was armed with high velocity rockets under the wings and a bomb bay that could hold 4,000 pounds of bombs, torpedoes or depth charges. Both were powered by a Pratt & Whitney R-2800-48W Double Wasp radial engine. Even though the workload was now split between two aircraft, the AF still tipped the scales as the largest single-propeller aircraft ever operated by the US Navy (it’s wingspan was 10 ft wider than the Douglas A-1 Skyraider, and the AF was a bit longer, but the Skyraider could carry twice the payload). The Guardian took its first flight in 1945 and entered service in 1950. A total of 389 aircraft were built, and in 1952 the AF-2W was upgraded by the addition of a MAD boom. This variant received the designation AF-3S.
Two pairs of AF-2W and AF-2S Guardians from Antisubmarine Squadron VS-24 fly in formation over Norfolk, Virginia in 1951. (US Navy photo)
While the one-two punch of the AF proved the hunter-killer concept, it was clearly just an interim measure, and the Guardian was only in service for five years. Guardian teams saw action in the Korean War performing maritime patrol missions, but the handling characteristics were generally poor and it suffered a high accident rate. The hunter-killer team was replaced by 1955 with the Grumman S-2 Tracker, the Navy’s first dedicated ASW carrier aircraft that housed both the hunter and killer roles in a single airframe. After retirement from the Navy, five AFs were flown by Aero Union to fight forest fires until their retirement in 1978. Five Guardians remain today, all of them the AF-2S killer variant: two are still airworthy; one is housed at the National Naval Aviation Museum in Pensacola, Florida; one is on display at the Pima Air Museum in Tucson, Arizona; and the other is displayed at the Commemorative Air Force facility in Mesa, Arizona.
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