Complex sentence: The W54 was tested for use in a U.S. Navy SEALs project that was demonstrated as feasible in the mid-to-late 1960s, designed to attack a harbor or other strategic location that could be accessed from the sea.
Split into simpler sentences: The W54 was tested for use in a U.S. Navy SEALs project that was demonstrated as feasible in the mid-to-late 1960s. Designed to attack a harbor or other strategic location that could be accessed from the sea.