The Grumman AF Guardian line became the United States Navy's first purpose-built, dedicated Anti-Submarine Warfare (ASW) aircraft when introduced in 1950. The series constituted two carrier-based airframe types to undertake two related battlefield roles - one to serve in the "hunter" role and the other to serve in the "killer" attack role. The type managed a relatively short operational service life with the USN before being retired in 1955 and was not exported. Production totaled 389 units.
Origins of the Guardian lay in a new torpedo bomber design of World War 2 (1939-1945) when the USN sought a successor for its classic Grumman TBF Avenger fleet. Initial work began in 1944 as the war raged on with the USN requirement calling for a large, well-armed aircraft utilizing the usual carrier qualities (reinforced undercarriage, folding wings, arrestor hook) and able to carry a bomb load of 3,600lbs. As a carrier-based system, range was also an important quality and the USN expected a minimum reach of 3,700 miles. The resulting design became the XTB2F but this development proved too large for American carriers of the period and the initiative was scrapped as soon as 1945.
Long-time USN aircraft supplier Grumman moved on a private venture initiative all their own which produced the company model "G-20". Engineers decided on a hybrid powerplant arrangement in which a conventional radial piston engine was fitted at front and a turbojet engine at rear - the combined approach providing the necessary power for carrier-launches and time-to-altitude. The radial engine of choice was the Pratt & Whitney "Double Wasp" series coupled with a Westinghouse 19XB turbojet engine. The fuselage arrangement was such that the crew of two would be seated under a canopy in a side-by-side format, sharing the workload of the aircraft. Its estimated war load was around 4,000lb with standard armament being 2 x 20mm cannons in the wings. An internal bomb bay could house anything from torpedoes to conventional drop bombs and depth charges. The undercarriage was of a "tail dragger" design consistent with carrier-based aircraft of the period.
Once brought to the attention of the USN, the promising G-20 was given the designation of XTB3F. However, the hybrid radial/turbojet arrangement was soon dropped as too impractical for the design scope. This produced the revised XTB3F-1S designation which covered the first flyable prototype. First flight of the series was finally attained on December 19th, 1945 though, by this time, the war was over and USN requirements began to evolve in the post-war world.
USN authorities now envisioned an all-new role for the XTB3F and this as a dedicated, carrier-based submarine hunter. However, the changes required of the aircraft - with all of the necessary technologies inherent in the sub-hunting role - could not be properly implemented to the Grumman airframe as was. This led to the decision to manufacture two models of the same make - one unarmed airframe (outfitted with sensitive equipment) to serve as the hunting platform and the other armed airframe as the strike platform. The aircraft would be fielded in unison and attack enemy submarines through a "one-two punch" approach. The search-and-track aircraft was given a revised internal arrangement to carry an additional two crewmen (for a total of four). It also sported a large, bulbous pod under its belly housing the APS-20 search radar. The engagement platform still carried the potent war load in its bomb bay but lost its strafing capabilities as the 20mm cannons were removed to save on weight and internal space.
The change in direction delayed the formal service entry of the line considerably for a first flight of a prototype was recorded until November 1948. Search aircraft were designated as XTB3F-1S while attack versions were XTB3F-2S. The -2S form went airborne for the first time in January of 1949.
Both were ultimately accepted after completing their trials. The -1S models were revised to the USN designation of AF-2W with the -2S models becoming the AF-2S. Both used the "Guardian" nickname over the courses of their respective careers. Service entry of the series was on September 27th, 1950 operating initially with squadron VS-24.
As completed, the aircraft designs were consistent with the aircraft of the period. The radial installation was held in the forward section of the aircraft and drove a large four-bladed propeller. The cockpit was just aft of the engine with a framed forward windscreen and a rearward sliding canopy. The fuselage spine was raised to accommodate the required internal fittings including mission equipment, bomb bay, and crew areas. Wing mainplanes were straight appendages with clipped tips and mid-mounted on the sides of the fuselage. The empennage was one of the more unique physical qualities of the Guardian, showcasing a traditional vertical tail fun with low-set horizontal planes but to these planes were fitted smaller vertical tail surfaces given the Guardian a tri-fin tail arrangement.
The aircraft carried a war load of up to 4,000lbs and this could be air-launched torpedoes, depth charged, and drop bombs. Working with the sub-hunter models, the attack versions could swoop in on enemy subs with lethal ordnance loads. Additional firepower support was given through 16 x 5" (127mm) HVAR (High-Velocity Aircraft Rockets), all held underwing.
153 examples of the radar-carrying, submarine-hunting AF-2W version were produced along with 193 examples of the AF-2S attack variant, both powered by P&W R-2800-48 radial engines of 2,400 horsepower. 1952 saw a third form - the AF-3S - introduced with brought about use of a retracting MAD (Magnetic Anomaly Detector) boom feature. 40 of this type further strengthened USN stocks. Final deliveries occurred in March of 1953. A proposed combination hunter-killer airframe - company model G-90 - by Grumman went nowhere.
The Guardian saw combat service during the Korean War (1950-1953) where it was used in the maritime (over-water) patrol role. The large aircraft were soon found to be clunky performers lacking the necessary power for the carrier role. This, and an abnormally high accident rate, did not endear the type to its pilots and crew and led to the series' short service life with the USN. Final forms were retired in August of 1955 with its replacement becoming the Grumman S2F "Tracker" line. Some Guardians remained in reserve until 1957 while others managed extended aerial lives as firefighting platforms into the 1970s.
For its time, the Guardian was the largest, single-engine carrier-based aircraft in operation. Its dimensions included a length of 43.3 feet, a wingspan of 60.7 feet, and a height of 16.1 feet. A preserved example is available for show at the National Naval Aviation Museum of Pensacola, Florida, USA where visitors can truly appreciate the size of this historical aircraft.