Eyes

Two powerful ships, round and small
Dart about with no ports to call,
Each in a tiny inland sea
Where very little water shakes
Except when the entire earth quakes.
Nothing easily can enter:
Swinging doors with self locking keys
Ready ever, day or night
To shield effectively both the seas
Which in shape and extent tally,
And set in a mini rift valley
That is halved by a narrow ridge.