There is some walking to explore the various sites, but generally Pearl Harbor is accessible to all fitness levels and mobility abilities. The tour even has a collapsible wheelchair that can be used as needed (although prefers to use it only for private tours); wheelchair participants must be pushed by someone in their party, not the guide.
However, the tour does try to cover a lot of ground in the time allotted, which means quite a bit of walking and being on one's feet. Built-in sitting time at Pearl Harbor only includes the 20 minute film, the boat ride to the Arizona, the van ride to/from Missouri, and ~30 minutes for lunch; the rest is generally on one's feet. Unless a private tour more customized to the group, shared tours usually end up 5-6 miles of total walking for the day. Tours are not able to drive guests directly up to the sites, so there is walking to even just get to a sight.
More specifically, the Bowfin submarine is a bit challenging with steps and narrow spaces, so those with limited mobility may need to sit out that part of the tour (~30 minutes). No wheelchair on the Bowfin.
Parts of the large Missouri battleship also have stairs and narrow spaces, but either the tour can focus on other areas (depending on the makeup of the tour group, and especially if it's a private tour) or split up momentarily if needed. Parts of the Missouri are wheelchair accessible, and there is even an elevator.
For the shared tour, it's important that the tour provide the full experience to all other participants. As a general test, it is recommended that shared tour participants be able to walk 300 yards without stopping. If this is not possible, the shared tour may not be a good fit for you. Or otherwise you may have to separate from the group for more frequent rests or to sit out some of the exploration on the Bowfin and Missouri.
For those with more limited abilities that are concerned whether the shared tour is a good fit, we recommend booking either a private tour, or our Pearl Harbor - Circle Island Combo tour which only includes the easier Arizona portion at Pearl Harbor, followed by a sightseeing tour by van around the island.
At the time of booking, there is a place at checkout to indicate any physical limitations.