The RN Coastal Forces Museum - which also seems to go under the titles of "Spitfires of the Sea" and "Night Hunters: Coastal Forces at War" is in Gosport - across the harbour from the Portsmouth Naval Base. Although it is within the perimeter of the larger RN Explosion Museum, and you can get in with the standard Portsmouth Dockyard ticket, it seems to have different opening hours, and a separate staff.You can get to the site via the ferry from Portsmouth Dockyard that is included in the Portsmouth Dockyard ticket - however that doesn't run very frequently. I went by car on a Sunday, and there was plenty of free parking in the area.It is located within a large historic boatshed by the water. Pride of place goes to two WW2 motor torpedo boats. MTB 71 is a 60' Vosper boat, originally ordered by Norway in May 1939, and requisitioned by the RN after the outbreak of war. MTB 331 was one of six boats ordered from Thornycroft by the Philippines in 1940 to the WW1 55' CMB design and taken over by the RN in August 1941. So, while they are near contemporaries, they are effectively from different generations of MTB design, and very different in appearance.The Coastal Forces Museum is relatively new - it only opened in 2021 and is very well done. They have extensive audio-visual presentations, and a good collection of artefacts, maps, documents etc on display in addition to the two boats. While you can't get onto the boats, they have a raised platform that you can access to get a good look at them from close. My only criticism is that the lighting made it quite difficult to get decent photographs from some angles - particularly of MTB 71.This museum is well worth visiting - but a visit needs to be planned, because they are only currently open 4 hrs/day, 5 days/week (closed on Monday & Tuesday). You also need to look for it, because the signage to get there from the Explosion entry could easily be missed.
Links and References:
National Museum of the Royal Navy: Coastal Forces Museum
The Night Hunters: The Royal Navy's Coastal Forces at War | National Museum of the Royal Navy