The big ones offshore are Subsea 7, Acergy, Technip, ISS/Bibby, Well-ops/Helix. Also Air Diving companies such as KD Marine, RBG Marine and Ot2K/Aquanos if they're still going. There's a few of Dutch companies such as Noordhoek, Bluestream Smit/GB etc and some other Windfarm and service/IRM companies who do bits n pieces on Semi-subs, such as Leco dive and Technodive in Norway.