Hi Pete! I did some research on this topic. There are number of "dunce cap" lighthouses in Japan (i.e.
Hiroshima, Fujisawa, Hakata Kō - most of them were build after 1950s)
I would say likely this picture is Yokohama South Outer Breakwater (built 1939).
Here are some other pictures of it:
LH Japan
yamatae.sakura.ne.jp



It has slightly different configuration of windows (but this could be due to tower reconstruction) but general shape of the tower, breakwater and square building nearby - everything is very similar. As far as I've found in internet - American troops were landed in Yokohama after surrender of Japan so this fits to story as well.
Hiroshima, Fujisawa, Hakata Kō - most of them were build after 1950s)
I would say likely this picture is Yokohama South Outer Breakwater (built 1939).
Here are some other pictures of it:
LH Japan
yamatae.sakura.ne.jp



It has slightly different configuration of windows (but this could be due to tower reconstruction) but general shape of the tower, breakwater and square building nearby - everything is very similar. As far as I've found in internet - American troops were landed in Yokohama after surrender of Japan so this fits to story as well.