Commercial diving and handling equipment.
Buy a suitable ship anywhere in Europe. A fishing trawler, an oilfield service vessel, etc. Just needs sonar and a suitable crane. There are tons of them.
The explosives could be straight from Ukraine. They have lots, notably old Naval mines and torpedoes, etc. But they could easily make a custom one too.
Ukraine has divers. Many work in contract gigs around the world.
Please send your theories to Seymour Hersh.
I’m sure he’ll follow up