From where he stood on the bridge Darrin could make out nothing for several minutes, though in the interval the lookout aloft reported that he could make out the "blimp" with surety, and that she appeared to be flying a signal, though he could not see what it was.
Then from the bridge the "blimp" became visible. A little later, too, the flag signal could be seen and read.
"Following another submarine," was what the signal said.
Going to starboard of the course Darrin advanced at ordinary speed to meet the "blimp," which, as in the former case, was flying just barely astern of the hidden monster, so that the forward British airman lookout could discern the shape of the craft that was being pursued.
Dave waited until the dirigible had passed. He then gave the order, "Full speed ahead," and came about behind the "blimp."
Leaping forward the "Grigsby" gave chase, the "blimp" at the same time moving up directly over the intended prey.
At the drop of the flag above, Darrin let go his right hand, the signalman transmitted the order, and the bomb rolled overboard.
As Dave's hand fell the watch officer advanced the lever of the engine-room telegraph. An extra jump was put into the speed.
Again a column of water rose astern, but this time there was only the normal explosion of the depth bomb.
"Good hit," said the dirigible, by radio, and the message was called up to the bridge. "Saw her stagger. She's done for."