Until right now, I wasn't even aware of these sailing cruise ships. Those are quite interesting! The largest two, Club Med 1 and Club Med 2 (the latter only completed in 1996) have a gross tonnage of almost 15,000 ts and are listed having a crew of around 214 and a capacity of 340-386 passengers, mostly in twin-beds. The staterooms look easily convertible to two double-racks or even six bunks in total. If you stack up in the state rooms in such a way and reduce the crew, i. e. the steward department, you can embark a light marine battalion.
Certainly they would have to make due almost without any land vehicles, but four medium sized barges can hang from davits. Deck space is a problem though, with only a small forecastle and not much space on the quarterdeck (i. e. the stern). I really don't see room for recoilless guns without some rebuilding, to be honest, mainly since the huge back-blast would make them dangerous to operate near walls and sails. Also, the range is not great on these guns, so Bofors 40 mm in single or dual mounts may be a better alternative. Light guns up to 30 mm as well as the venerale Bofors also enjoy the benefit of not needing barbettes, i. e. they could be bolted directly on decks without punching through the construction. That makes retrofitting much easier.
One probably could raze the light structures on Star Deck - mainly a glass superstructure housing a restaurant - in order to create more deck space for crans, boats, vehicles, containers and light artillery. A great feature of both ships however is the water sports platform, which is essentially a miniature well deck/dock and can be used to disembark marines quickly for boarding parties etc. There is also room for small-craft.
The big question for these ships constructed by Société nouvelle des ateliers et chantiers du Havre will be, how there computers have weathered nuclear war. The ships cannot be sailed manually without significant modifications to the standing rigging. The masts are not meant to be climbed easily and the crew complement does not support a traditional sailing crew, without significantly reducing the number of passengers. So, if the computers are fried, e. g. by EMP, those ships become slow steamers, 10 to 12 knots with engines only, compared to 15 kn under combined (sailing and steaming) propulsion.
Deckplan:
https://www.windstarcruises.com/Blan...f_10-22-20.pdf