sea power 
noun [mass noun]
A country’s naval strength, especially as a weapon of war: centuries of freedom from foreign occupation behind the barrier of sea power British sea power...
- Much of their explanation of the strategic utility of navies and of sea power is as valid today as it was a century ago.
- In that context, sea power is really only relevant to the extent that it influences events elsewhere.
- Britain owed its survival in this long struggle to its national determination to keep fighting, to its financial strength and to its sea power.