There are more conversions possible than I could try to list here, but unfortunately an attack transport is not one of them. APAs and AKAs were converted from faster ships, while the Liberty ships were employed in roles where speed was less of an issue. To give you an idea of the number of possibilities here is a quick list of types where the Navy employed Liberty ships (WWII and postwar):
AG
AGM/T-AGM
AGR/YAGR
AK
AKN
AKS
AP
AR
ARG
ARV
AVS
AW
IX
T-AKV
YAG
For wartime merchant ships, you can do conversions to represent ships other than the O’Brien. There were actually a lot of differences between ships, with details such as gun tubs changing from yard to yard. There were also a variety of defense systems that were employed on these ships, with the most common being torpedo nets.
Another possibility is to do another variant of the Liberty ship. There were actually several types of Liberty ships built, all of which shared a common hull and machinery. These include tank or boxed aircraft transports, tankers, and colliers. Add to these postwar civilian and government modifications. In commercial use they often had changes done to the superstructure, and were even enlarged by welding in new sections of hull. Liberty ships have been employed in just about every conceivable use, including container ships, pipe and cable layers, mine testing ship (powered by four aircraft turbo-prop engines mounted on pylons!), barges, floating piers, fish processing plants, and even as a floating nuclear power plant.
Basically if you collect all the variants of all 2,710 of the Liberty ships, you easily have more than 10,000 conversions (some minor, some not) that are possible. This does not even take into account the other classes of ships used by allied nations with essentially the same hull, such as the Oceans, Forts, and Parks.
Regards,
Chris Friedenbach
Crewmember, SS Jeremiah O’Brien.