Characteristic it was of Tom Swift to act calmly in times of stress and danger, and he ran true to form now. Only for an instant did he show any sign of perturbation. Then with calmness and deliberation the young inventor quickly did a number of things to the controls within his reach.

First of all he signaled to the engine room that he was going to take charge of the boat. This meant that the navigator in the conning tower was to keep his hands off the various levers and wheel-valves. It was possible to operate the M. N. 1 from three positions, but Tom wanted no triplicate handling of his craft now.

Almost the instant Tom signaled that he would take charge back came flashing the electrical signal from the conning tower that his orders were understood. The next thing that those aboard the craft became aware of was a tremor that seemed to run through the whole under-sea ship. The quiet had changed to a subdued humming, and the ominous lack of motion was succeeded by violent vibration.

"Backing her up, Tom?" asked Ned, in a low voice.

"Trying to," was the answer. "But I'm afraid her nose has gone in pretty deep. I've reversed the propellers."

For perhaps a minute this vibration continued, showing that the powerful electric motors were turning over the twin propellers at the blunt stern of the craft. But she did not change her position.

With a touch of his hand, and still almost as cool as the proverbial cucumber (though why they should be cool it is hard to say), Tom stopped the motors. Once again the craft was quiet, but now, instead of the occupants being able to see clearly from the thick, glass windows in the forward cabin, the water showed muddy and murky in the glare of the underwater searchlight.

"Bless my postage stamps, Tom! what has happened?" exclaimed Mr. Damon. "Has a giant squid attacked us, as one did some time ago, and is he roiling up the water?"

"No, it isn't a squid, Mr. Damon," replied the young inventor easily; "though the water does look as if a squid had spilled a lot of his ink in it. This is just the effect of mud stirred up by our propellers. There may be more of it."

Ned looked toward Mr. Hardley to see how he was taking it. The seeker after gold apparently had good control of his nerves, or else he was ignorant of what was going on. For he asked, casually enough:

"Have we stopped?"

"We have," answered Tom. "I thought I'd give you a view of the scenery."

Perhaps he spoke sarcastically, but, if he did, Mr. Damon's friend did not seem to be aware of it. Coolly enough he replied:

"Well, if this is a fair sample of underwater scenery I prefer something up above, though I appreciate that this may be needful."

"We'll soon be traveling along," announced Tom. "Koku," he added to the giant, who had been calmly sitting during the excitement, "go to the engine room and help with the big levers."

"Yes, Master," was the answer. Koku had implicit faith in Tom.

Waiting a moment for his faithful servant to reach the post assigned to him, Tom again signaled to his helpers and then quickly turned a wheel which produced startling results. For all within the submarine suddenly slid forward across the cabin floor.

"Bless my hammock hooks, Tom! are you standing her on her head?" cried Mr. Damon.

"That's exactly what I'm doing," was the answer. "I've started to empty one of the after ballast tanks, and that, naturally, raises the stern while the nose is held down."

The submarine was indeed in a peculiar position. She was on a slant in the water, her nose held fast in the soft mud bank, and it was Tom's idea that by making the stern buoyant it might help to pull her free.

To this end he also gave what assistance the propellers were capable of adding by starting the motors again, so that the craft once more trembled and vibrated.

But it all seemed to no purpose. Aside from the slanting position, there was no change in the M. N. 1. Ned, looking out into the murky water, which had cleared slightly, saw that the craft was still held fast. And then, for the first time, Mr. Hardley seemed to become aware that something serious was the matter. Up to now he seemed to think that all that had occurred was done for the purpose of testing the newly outfitted underseas boat.

"Is there anything wrong?" he asked sharply of Tom. "Why are we in this position, and why don't we go on out to the open ocean and make a test at considerable depth? We'll have to go down deeper than this if we find the Pandora!"

"I suppose so," agreed Tom. "But we have had an accident, and--"

"An accident!" interrupted the gold-seeker, and then Ned saw him turn pale. "Do you mean to say this is not part of the test?"

"We have run into a mud bank," said Tom. "The steersman must have become confused, or else, since we last used the submarine, there has been a shift of the mud banks in this river and one exists where there was none before. At any rate, we ran our nose deep into it, and here we are--stuck!"

"Can't we get loose--go up to the surface?" demanded Mr. Hardley.

"I'm trying to bring that about," announced Tom calmly. "So far her engines haven't been able to pull her loose."

"But Great Scott, man, we can't stay here!" cried the now excited adventurer. "We'll be drowned like rats in a trap! Let me out! Isn't there some way? I'll be shot through a torpedo tube, if necessary! I must get out! I can't stay here to be drowned! I have too much at stake!"

"Now wait a minute!" calmly advised Tom Swift. "You haven't any more at stake than the rest of us. None of us wants to be drowned, and there is only a remote possibility that we shall be. I haven't played all my cards yet. We can live on this boat for a week, if need be."

"You mean under water as we are now?" asked Mr. Hardley.

"Yes. I always keep the boat provisioned and with plenty of air and water for a long stay, if need be," replied Tom. "And I did not overlook the fact that we might have an accident on the trial trip."

"I don't see how you let an accident happen before we even got started," complained the gold-seeker. "I should think your steersman would have been more careful."

"He is very careful," explained Tom. "But we have not used the craft for some time, and, meanwhile, there have been changes in the river, due, I suppose, to heavy tides. But we may get out of the grip of the mud bank soon."

"And if we don't, what then?" asked Mr. Hardley.

"Then there is always the torpedo tube," said Tom calmly. "And we are not very deep down. I think I can save you all."

"I certainly hope so!" was the fretful comment of the adventurer. "I have too much at stake to be drowned like a rat in a trap! You must send me up first if it becomes necessary to use the tube."

Tom did not answer. But as he looked out of the observation windows to see if possible the conformation of the mud bank, the young inventor whispered to Ned one word. And that word was:

"Yellow!"

"You said it!" was Ned's whispered rejoinder.

Tom Swift arrived at a sudden determination. Once again the motors were stopped, and the boat gradually assumed an even keel.

"What are you going to try, Tom?" asked Ned.

"I'm going to shove her farther into the mud bank," announced the young inventor. "I think that's the only way to get her loose."

"Bless my apple pie, Tom!" cried Mr. Damon, "doesn't that seem a foolish thing to do?"

"It's the only thing to do, I believe," was the answer. "This mud is of a peculiar sticky and holding kind. The sub's nose is in it like a peg in a hole. What I propose to do now is to enlarge the hole, and then our nose will come loose--I hope."

"But you haven't any right to shove our nose further in!" cried Mr. Hardley. "I won't allow it! I demand to be put on the surface! I won't be drowned down here before I get the gold that's coming to me--the gold and--"

"Now look here!" suddenly cried Tom. "I'm in command of this boat, and you'll do as I say. I'll gladly set you on the surface if I can, and this is the only way it can be brought about--it's the only way to save all of us. I'm going to enlarge the mud hole so we can pull out. Please keep still!"

Mr. Hardley stared at the young inventor a moment, seemed about to say something, and then changed his mind.

"Hold fast, everybody!" suddenly called Tom. The next moment the M. N. 1 began behaving in a most peculiar manner.

She appeared to be acting like a corkscrew. While her bow was comparatively steady, her stern described a circle in the water which was churned to mud by the two propellers, each being revolved in a different direction.

"I'm trying to make the hole bigger just as an amateur carpenter makes a nail hole bigger, so he can pull out the nail, by twisting it around," explained Tom. "The motion may be a bit unpleasant, but it is needful."

And indeed the motion was unpleasant. Tom, veteran airman and sailor that he was, began to feel a trifle seasick, and Hr. Hardley was in very evident distress.

Suddenly, however, something happened. The M. N. 1 gave a lurch to one side and then shot upward so quickly that Ned and Mr. Damon lost their balance and slumped over on the bench that ran around three sides of the room.

"Are we free?" cried Mr. Hardley.

"We have come loose from the mud bank," said Tom quietly. "By boring into it the hole was enlarged sufficiently to enable us to pull loose. There is no more danger!"

His announcement was received in momentary silence, and then Ned exclaimed:

"Hurray!"

"Bless my accident policy!" voiced Mr. Damon.

Mr. Hardley appeared dazed, and then, as the submarine was again moving through the water, seemingly none the worse for the accident, the gold seeker approached Tom Swift.

"I want to apologize, Mr. Swift, for my actions and words," said Mr. Hardley frankly. "I admit that I lost my head. But it's my first trip in a submarine."

"I realize that," said Tom, equally frank, "and we'll forget all about it. It was a strain on you--on all of us--though there really was no very great danger. Now, are you game enough to continue the trip?"

"Try me!" exclaimed the adventurer. "You won't find me acting so like a baby again."

Nor did he, even when the craft reached the open ocean and went down to a considerable depth, where, had any accident occurred, there would have been grave danger to all. But Mr. Hardley seemed to enjoy it.

"Maybe I've misjudged him," Tom said to Ned, when they were getting ready to go back.

"It's possible," agreed the financial manager. This trial, which so nearly ended disastrously, was only one of several. No damage resulted from the collision with the river mud bank, and that trip and the ones following gave Tom some new ideas in interior construction which he followed out.

About a month later all was ready for the trip to the West Indies to look for the ill-fated Pandora. Tom's affairs were put in shape, the submarine was laden with stores and provisions, the new diving bell and other wonderful apparatus were put aboard, and the crew and officers picked. Ned, Mr. Damon, Koku, and Tom were, of course, together, and though Mr. Hardley was a stranger, he seemed to become more friendly as the days passed.

"Well, we start in the morning," said Tom to Ned one evening. "I'm going over to tell Mary goodbye."

"Give her my regards," requested Ned, and Tom said he would.