We all know the story in the Book of Mormon of the Jaredites building their barges and sailing over to the promised land. Often I hear their ships referred to as a kind of submarine, or compared to a submarine at least, and that really is not correct at all.
We get our first detailed description of the ships in Ether 2
16 And the Lord said: Go to work and build, after the manner of barges which ye have hitherto built. And it came to pass that the brother of Jared did go to work, and also his brethren, and built barges after the manner which they had built, according to the instructions of the Lord. And they were small, and they were light upon the water, even like unto the lightness of a fowl upon the water.17 And they were built after a manner that they were exceedingly tight, even that they would hold water like unto a dish; and the bottom thereof was tight like unto a dish; and the sides thereof were tight like unto a dish; and the ends thereof were peaked; and the top thereof was tight like unto a dish; and the length thereof was the length of a tree; and the door thereof, when it was shut, was tight like unto a dish.
While the shape may somewhat resemble a modern day submarine, it seems pretty clear that these were very buoyant watercraft. Also there is no mention of any kind of apparatus for adjusting the buoyancy of the barge. While there was an opening at the top for air, and one at the bottom (presumably for waste removal and also perhaps to allow some fishing en route) the only way to use these for buoyancy control would be to open both stoppers at the same time and sink the ship to the bottom of the sea.
The way they sailed to their promised land also runs counter to what would be true if these vessels were some kind of submarine. In Ether 6 we read:
5 And it came to pass that the Lord God caused that there should be a furious wind blow upon the face of the waters, towards the promised land; and thus they were tossed upon the waves of the sea before the wind.
6 And it came to pass that they were many times buried in the depths of the sea, because of the mountain waves which broke upon them, and also the great and terrible tempests which were caused by the fierceness of the wind.
7 And it came to pass that when they were buried in the deep there was no water that could hurt them, their vessels being tight like unto a dish, and also they were tight like unto the ark of Noah; therefore when they were encompassed about by many waters they did cry unto the Lord, and he did bring them forth again upon the top of the waters.
Their barges clearly did not travel underwater, but on the surface where the wind was able to move and direct them to their destination. The storm that accompanied the wind caused huge waves to wash over them, and to briefly drive them below the surface, but the ship was designed to withstand it and return them to the surface as soon as possible.
Calling the Jaredite barges a kind of ancient submarine makes it harder for sincere, intelligent people to take the Book of Mormon seriously. Some anti-Mormons go out of their way to portray these ships as submarines so they can set up a straw man they can use to attack and mock the Book of Mormon. When we start talking of it in the same way we help them, not the Lord. If a comparison must be made to a modern boat, it would be a far better match to compare them to a large kayak rather than a submarine.