Sounds like the old US Navy method of naming helos HSS-1 = Helicopter (H), Anti-sub (S) , Sikorsky (S), 1st model (-1) which was the H-34. The HSS-2 was the SH-3, thank God they dropped the system, else the Sea Hawk would have been the HSS-3.
By the time you decoded the name, you could have bought a book about it.