This is a Bad Thing to do. It is perfectly fine to practice attacks, but not on the ships of another nation. Mistakes can happen and people might die. Such conduct is prohibited by international agreements.

For example, the 1972 US/Soviet Agreement on Prevention of Incidents at Sea states:

Commanders of aircraft of the Parties shall use the greatest caution and prudence in approaching aircraft and ships of the other Party operating on and over the high seas, in particular, ships engaged in launching or landing aircraft, and in the interest of mutual safety shall not permit: simulated attacks by the simulated use of weapons against aircraft and ships, or performance of various aerobatics over ships, or dropping various objects near them in such a manner as to be hazardous to ships or to constitute a hazard to navigation.