4:30
asked Frank . `` From the top of her periscope to the bottom of her keel , '' replied Captain Nicholson , `` the Y-3 displaces exactly 20 feet . It will be ticklish work to navigate in those six and a half fathoms -LRB- 39 feet -RRB- without being drawn down by suction and striking bottom so hard as to rebound up to the surface , where the Turks are sure to see us . '' At 4:30 o'clock in the morning there was light enough to make out the small gray fort guarding the entrance to the Euphrates . The submarine did not lie more than a mile away . `` It 's up to us to get out of sight before the fort watchers see us , '' said Captain Nicholson . Being satisfied of how far his run should be and verifying his course by the compass while still on the surface , Captain Nicholson quickly ordered the vessel trimmed down to a depth of 60 feet , and then started forward at about four knots -- as low a speed as was consistent with good handling .