The Galarra class - conceptualized in the wake of the Second World War and built as a modern escort for carrier groups, to serve as air-direction vessels or pickets as required, a series of sixteen were built, replacing the worn pre-war small cruiser force as leaders for the large fleet destroyer flotillas. They proved unwieldy in the ASW role, and had to serve in second-line roles all the way into the start of the major fleet modernizations of the 1980's.
Seventeen of these vessels were built - something the Navy is still believed to regret. Only two were completed in their original SSRN role - their large size and commodious internal space once the second reactor plant was removed saw a second role - carrying spare nuclear weapons and crews for the Navy's seaplane heavy bomber force to re-arm for a second strike, and refuel via pre-positioned submerged fuel tanks in various deserted atolls throughout the Pacific. They left service with the end of the Cold War, by which time they were regarded as being approximately as survivable against the Soviet and American SSN forces during transit as a donut in an American police station. The last five completed as the Navy's first SSBNs, carrying their missiles in the former forward reactor and engine compartments.
The far more 'rational' use of nuclear power for submarines, these were the first hunter-killer/commerce attack submarines built using the new technology. Quieter than Soviet boats, and competitive with early American craft, they did not begin to leave service until the 80's, as further upgrades to their deteriorating propulsion systems were deemed to be a waste of ship repair funding.
With the growing threat posed by Soviet and American strategic forces, the second-generation submarine program was hurriedly re-oriented to produce a more survivable SSBN - even being refitted, the Gawuras would never be optimal in their ability to hide - a total of seven were built to provide four on patrol at any given time.
The attack submarine counterpart to the Vigilant-class, named for the cruiser that was ingloriously piled onto a reef during a typhoon in 1963. These boats were worked gently starting in the 1990's onwards, as submarine priorities rapidly entered a period of massive flux.
With the first units laid down in the mid 1980's, the first tranche of seven boats replaced the Gawura SSBNs - the second tranche replaced the land-based ICBM force in the face of the inability to sufficiently harden the two wings in the face of a first strike. (Echoing the debates over MX in the United States.) This decision, taken late in 1990, threw havoc into the submarine building program, delaying the next SSN, and seeing the planned SSK brought forward and increased to twelve boats.
Stationed in four three-boat stations throughout the Empire, these boats, built from the late 1980's onwards, provide defence of choke points leading into Californian home waters - Tierra del Fuego, Larrakia (OTL Darwin), Persian Gulf, Red Sea.
Heirs to a storied lineage, these large, expensive SSNs did not enter production until the Rays of Dawn were completed - intended for a 1991 order, this slipped to 1999 - they are now replacing the Galarras, of which a dozen remain in service. A total of thirty vessels to this basic design are intended to be built, though wide differences between the currently planned three main batches is expected.