"About two miles off yet!" he muttered.
The chart gave the bottom on the sandbar in front of the entrance as shell and hard sand.
"Lucky," Captain Nicholson told the boys when he returned to the bridge. "This will allow us to run with very little under our keel in no fear of rocks."
"Is it very deep along here?" asked Jack.
"No," replied the commander. "That's what worries me. The chart shows a bare six and a half fathoms over the bar, continuing slightly deeper until it sheers off into the deep basin that is the inner harbor."
"And how much water does the Y-3 draw?"' 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 (39 feet) 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.