The advantage of being able to change crews at sea may not be quite as clear. This, however, grows out of the fact that today’s non-rigid airship has greater endurance than the crew which flies it. An anti-submarine, anti-mine patrol calls for constant alertness. Reduction of vibration and noise, the use of closed cars instead of open cockpits has lessened fatigue, enabling men to remain on duty over longer periods than before. But obviously there are limits. The Navy is conservative in estimating how long its new “K” ships may stay out without refueling. Weather and the nature of the mission will have some bearing on that, but if we assume a cruise of 48, 60 or even 72 hours which might be done under favorable conditions and idling the motors, we still cannot expect a crew of men to remain vigilant and alert for that length of time. Extra men for relief watches can be carried only at the expense of the fuel load. However, if a fresh crew could be sent aboard every 12 hours from a nearby surface ship, along with fuel, ballast and supplies, the blimps might operate for extended periods. No blimps have done this. The fleet might see no need for them to go out for long periods. However, the possibility has been established, and might be useful in the emergencies of war, or accident. While the primary usefulness of the blimp lies in the coastal waters, it can go to sea if needed—and stay out—can be used in convoy work or as a listening post. Other improvements were uncovered during the experiments. A sea anchor or drogue was devised to enable the airship to “lay to” for extended periods, without consuming fuel, in case it wishes to use its listening devices against submarines, make repairs or for other purposes. Plans have been worked out for landing on the water in quiet bays in calm weather, utilizing flotation gear, or a three-point mooring to ordinary mud anchors—facilitating servicing from nearby Coast Guard stations. Perhaps a significant thing about these experiments is that the principles seem applicable as well to rigid airships. The ability to pick up ballast in flight may well eliminate the necessity for ballast-recovery devices, with a substantial saving in cost, and an impressive saving in weight. By eliminating the heavy condensers, and translating that weight-saving into fuel, it is estimated that the range of a ship of the Los Angeles size could be increased by 20 percent and ships of the Akron-Macon size by 15 percent, in the last case amounting to 1,250 miles of additional cruising radius. A trans-oceanic passenger airship could start out with virtually no water ballast at all except a minimum amount for maneuvering, use its fuel supply as ballast and pick up sea water as needed. This could be done at 500 feet elevation, at the rate of 80 gallons a minute, using a 30 horsepower motor, could be done in half an hour a day. The ship need not slow down materially while doing this.