How are deep sea vehicles recovered from the sea-floor?

Before we put them in the sea, we set all the cameras up to run on a time lapse more than we have our system whereby we attach three 40kg steel weights and then we deploy it over the side and the steel weights make it entirely negatively buoyant. It still takes about 4½ hours in complete freefall to get to 10,000 metres because remember that depth is about the same altitude as a jumbo jet will fly, so it's a long way to go. It crash lands on the bottom and then we decide that it's enough, maybe 12 or 24 hours later, we have devices on the land called acoustic releases and they are holding the steel weights. So each one has a unique number like a phone number and you just call it and say it releases the weights. It understands it over quite a long distance and then drops the weights, and we have floatation devices on the top of it that bring it back to the surface. So it's pretty simple. Expensive, but the principle is simple.