Alan Erskine wrote:

The first purpose-built ASW aircraft was the Grumman AF Guardian, it
preceded the S designation for such aircraft. The second purpose-built
ASW aircraft was the Grumman S2F Tracker. It was
designated S2F because it was the second ASW aircraft built for the
Navy by Grumman. With the Tri-Service designation system the S2F
became the S-2. Why not S-1? Probably just to keep things as simple
as possible.

I think the AF was already out of service in the USN by the time the
designation system was changed; that might explain the abscense of the
"S-1".


That sounds like a good reason not to redesignate an aircraft to me, but the
DoD didn't agree. The Convair F2Y Sea Dart was redesignated F-7 under the
Tri-Service designation system, five years after the program was canceled.