Mr. Bilverstone put over the tiller, so that the boat yawed and her sail began to flutter. He left the tiller and crept forward over the thwarts, seized the halliard, and lowered the sail, then hauled it up again, returned to the tiller and brought her up to the wind, going on as before.
"What did you do that for, sir?" Seth inquired, amazed at what he took to be an example of bad seamanship. "She was going on all right."
Mr. Bilverstone took a drink of tea.
"It was a signal," he explained. "All the time while we've been out they've been watching us from the naval base. The Kingfisher has had her steam up ready to come out as soon as we should give the sign. We have given it. You will see her presently. What about the periscopes?"
"They're still there, sir," Seth answered. "I can see the top of her conning-tower above water. She's moving. I believe I can hear her engines grunting. So she's got some petrol left. Hullo! I can see a man's head and shoulders."
"She's bound to come up and work her petrol engines to generate electricity," said Mr. Bilverstone, going on a fresh tack. "Haul in the net, quick! Those Germans will guess we had a hand in it when they see the gunboat coming after them."
Seth got the gear inboard, and again his companion tacked. The boat was making for home, with both wind and tide in her favour.
Mr. Bilverstone could now watch the submarine. She was awash, and her petrol engines, making a great clatter, were evidently working up to full speed. Two of her crew had come out on the platform of her conning-tower. One was in officer's uniform. The sun, piercing the mist, shone upon his brass buttons and the gold badge on his cap. He stood looking southward to where two plumes of smoke from a steamer's funnels rose into the morning air over the lighthouse point. It could be seen that he had his left arm in a sling.
"She's coming after us, sir!" cried Seth. "She'll sink us!"
"She's trying to escape from the gunboat," declared Mr. Bilverstone. "You see, she can't submerge until her electric batteries are charged, and she can go quicker on the surface. Look! There comes the Kingfisher!"