[Zancarius]

I had no idea we used concrete ships during WWII until I found out we sunk one during the atomic testing in the Pacific.

The US used a concrete ship (YO-160) [1] as one of the target/target vessels during the Operation Crossroads tests [2]. The ship had been used as an oiler/fuel barge during WWII and sunk not from the tests directly but from damage sustained when moving it after the Able test. Although the Baker shot served as a coup de grâce (ultimately sinking the vessel), YO-160 was already taking on water and probably would have sunk on its own.

[1] https://en.wikipedia.org/wiki/YO-160

[2] https://www.youtube.com/watch?v=xGQkTDStnx0&t=22m36s