My daughter took these shots today at Flamingo Beach on Culebra Island off Puerto Rico. Training vehicle from WWII?
I think they may have been training vehicles for the Korean War. My brother-in-law served on Marine armor in Korea. He told us that he trained on Vieques Island, which is near Culebra Island. In fact at the time the movie Battlecry with Van Heflin and Aldo Ray was being filmed there. They used footage of his tanks that was used in the movie. He still remembered that his tank was C-4. We even held a Battlecry party at our house and screened the footage from the film, all 10 seconds!
There was a Naval base and extensive firing range at Cuebra, sea to shore in parts, c.1941 -1975. These ex US Marine M4A3 105's used as targets were not considered worth extracting. There is debate as to whether they were moved to the beach to make them less accessible then or just left in-situ.
Thanks for the confirming details. It is interesting how my daughter came across this and reestablished this family memory.