English Russia has this post about how a naval weapon test station was constructed in the Caspian Sea. Though impaired by the wavy sea (the wave height during a storm in Caspian sea could reach 7.5-8.0 m) and abandoned, the structure remains untoppled after over half a century. The construction of the foundation, is quite a engineering masterpiece even for today’s standard:
The entire underwater part of the gigantic construction, called “Massive”, was built on the shore in the foundation pit with a capacity of 530,000 cubic meters. Sometimes they even dug by hand, but more often dredgers were used.
On the bottom of the foundation pit a huge ferroconcrete “box” was built, measuring 14 meters high. Next, the plate separating the pit from the sea was destroyed and the surfaced “box” was dragged to the building site of the station. There, in 1935, the “box” was filled with water and placed on the specially site, which was made of quarry stone. Thereafter construction of the station was done in a usual way, with people and materials being delivered by ships.