<p>An underwater "submarin" 
</p>
This one is used for deep sea work. I guess this is the smallest manned submarine/rov in the world.
<a rel="nofollow" class="external text" href="https://www.flickr.com/people/21110936@N05">bengt-re</a> from Sweden
CC BY 2.0
<a rel="nofollow" class="external text" href="https://www.flickr.com/photos/bengt-re/2071298767/">ROV but you can be in it....</a>