In June 1971, McDonnell Douglas was awarded the prime contract for
Harpoon, and the first test missile flew in October 1972.
By that time it had already been decided to develop air-launched, ship-launched and submarine-launched Harpoon variants, designated
AGM-84A,
RGM-84A and
UGM-84A, respectively.
The UGM-84A became operational on attack submarines in 1981.
RGM-84A
For launch from submarines, the UGM-84A is enclosed in a capsule, which glides to the surface after launch from the torpedo tube. When the capsule breaks the surface, the front and end caps are ejected and the missile fired. The digital MK 117 Fire Control System has full support for
Harpoon integrated.
The
UGM-84B is a UGM-84A variant for use by the Royal Navy, and flies at a slightly lower cruising altitude than the -84A. The UGM-84B is called GWS-60 by the Royal Navy, and the
UTM-84B is the corresponding training version. Interestingly, the designations
AGM-84B,
RGM-84B,
ATM-84B and
RTM-84B were also formally allocated, although no air- or ship-launched -84B missiles were ever built.
The next U.S. Navy variant was the
Harpoon Block 1B, designated
AGM-84C,
RGM-84C and
UGM-84C. The Block 1B missiles were first delivered to the Navy in June 1982. The
xGM-84C flies at the same lower cruise altitude as the UGM-84B, and does no pop-up manoeuver, flying a sea-skimming attack profile instead. The Block 1B training missiles are the
ATM-84C,
RTM-84C and
UTM-84C.
http://www.designation-systems.net/dusrm/m-84.html