> Coast Guard helicopter with a mounted machine gun pointed at me and a Coast Guard response (defender class) boat with a .50-caliber machine gun also fixed on me while they sat off our bow.
Why'd they do that?
> they said I should hold my position and not move.
Why?
> The sub came out with two large ships on each side with blast shields on the each ship.
...why?
When a $2,000,000,000 Ohio class submarine carrying ballistic missiles is most vulnerable leaving port moving towards water deep enough to dive in. The Coast Guard is tasked with keeping all potential threats away. The ships on the side would protect the submarine from RPG and similar attacks while the submarine is surfaced.
Safety and security. A small boat can be a threat and cause damage to a larger boat if you let it get close enough. Small boats can easily capsize if they get too close to a larger boat.