What began as a successor to the Avenger torpedo bomber of World War II ended up becoming the Grumman AF Guardian, the US Navy's first dedicated anti submarine aircraft to enter service. The Guardian came in two versions: the 'hunter' featured a large radome under the fuselage plus additional crew members operating the detection gear; the 'killer' had a smaller radar in an underwing pod and provision for bombs or depth charges in an internal bay. In practice it was necessary for both of these to operate together as 'hunter-killer' pairs, one charged with detection task and the other performing the actual attack. Guardians saw action during the Korean War (mostly as patrol aircraft) and were constantly upgraded to the point that some had magnetic anomaly detectors (MAD) in a starboard fuselage mounted boom. They were retired in 1955 and replaced by the S-2.

The first prototype XTB3F-1 flew on 19 December 1945, its designation reflecting the fact it was still intended to be a torpedo bomber until renamed AF for its new ASW role. The AF-2W was the 'hunter' version while the AF-2S was the 'killer' as mentioned above. AF-2 units were later fitted with MAD gear but retained their designation.