During the campaign, Wainwright protected the transports from enemy air and submarine activity.

Ray described submarine activity as best he could.

Its waterfront now teems with train, ferry and submarine activity.

Japanese radio intercepts did notice an increase in both American submarine activity and message traffic.

I don't like submarine activity among the towelheads, right?

After the exercises, that night the fleet remained at sea on patrol even though submarine activity had been reported in the area.

The threat board showed no known submarine activity in the immediate area, a datum to be taken with a considerable bit of skepticism.

However, submarine activity soon returned and full patrols were resumed in early February.

Keeping an eye on their submarine activity would be difficult enough.

But here there was a strange thing: the Gnorri were unobstructed in their submarine activities!