e code messages and the radio man could not decode them because
the first thing the steamer captain had done that morning when it looked
as though the U-boat was going to make them take to the boats was to
heave the code-books overboard. In the morning they would know.

Morning came, but with it not a ship in sight. Of twenty ships and a
group of destroyers the night before, not one now. It was his
signal-officer who thought it out first. "U-boats thick last night, sir,
and the convoy must 'a' got orders to disperse or else change course,"
he said to the doctor.

"That sounds like good dope to me too." He turned to the steamer's
captain. "Where were you bound, sir?"

"To Havre."

The doctor could see nothing else but to proceed to Havre, and on a
zigzag course. The old captain did not know about the zigzagging; he had
never done any zigzagging and did not know why he should now--besides,
it mixed his reckoning all up.

The doctor said he would fix the zigzagging part of it, and, telling his
hospital steward to have a special eye out for the very sick man, went
into the chart house and proceeded to explain the zigzagging stuff. He
paused to recall all he had ever learned while elbowing the 352's
navigator over the chart-table; also the answers he had got to his
questions while so doing.

You steer 45 degrees off the course you really want to make for so many
minutes and then you steer 90 degrees from that for the same number of
minutes back toward the course you really want to make--see, so--and
that gives so many minutes to the good--see. That was one way.

"How many minutes?" asked the captain.

Doc had to stop and think that over. "Twice the square of the total
minutes--no, no. Take twice the sum of the squares of the minutes on the
two legs--and get the square root and then you have the hypothenuse of
the two sides of the triangle; that is, you have the number of minutes'
steaming you make good on your real course."

The old skipper knew nothing of square roots or hypothenuses or anything
that looked like 'em, and he had always laid his course out by compass
points.

"All right," said Doc, and after a while laid out the zigzag courses in
compass points.

The old fellow did not quite like it, so all that day Doc alternated
between his bad patient and the bridge to keep the skipper reassured
about the zigzagging. Also he urged the crew to have a special watch out
for U-boats.

That night Doc and the sea