Well actually it would have to be a special design. Waterways for coolant to flow, etc.
Think like combustion engine cooling design.

The only submerged brush type motors I am familiar with are gas tank fuel pumps. Submerged in gasoline is a special case.

 

Submerged in gasoline is a special case.

What is special about it? Gas is not a conductor.

 

What is special about it? Gas is not a conductor.

And water isn’t normally explosive. A spark in water is less dangerous than one in gas.

 

Submerged in gasoline with no air available does not usually a problem. But certainly a brush-motor in a gas tank is a special case. The various classifications of hazardous conditions versus electrical circuits will clarify that.

 

But certainly a brush-motor in a gas tank is a special case.

Can tell you've never changed an intank fuel pump.

 

And water isn’t normally explosive.

But water is conductive.