I wouldn't call it strange. Naval combat wasn't a priority so there's no point in making assets for something with no direct effect on gameplay.

@Mr Zurkon But in Merc 2, there are naval surface vessels and a drivable Bladesong missile boat. So it maybe that Merc 1 has not yet considered designing the combat section of naval surface vessels.

Yeah but to be fair, mercs 2 has tons of more open water so it makes sense to let the player swim and use navel ships, while in mercs 2 there are only a few bodies of water and rivers at best