The army is a special place. Those who have not served, with a high degree of probability, will not be able to understand some of the military things, or at least to become familiar with them. One of these funny things is, of course, the rude and extremely eloquent army slang. Military people are generally very cunning in invention in this regard. For example, what is only the expression of tankers "to catch a dolphin" is worth.
The expression "to catch a dolphin" is true not only for tankers, but for almost all mechanics-drivers of armored vehicles with a low side. This jargon appeared in the days of the Soviet Union. Surely everyone had at least once to see funny photos with tankers, who are completely smeared with mud, on the Internet. Actually, this state of the crew members is the result of "catching a dolphin". There is little pleasant in this, but there is nothing terrible either, at least for a person.
The dolphin is very simple. This is due to Archimedes' law on the displacement of liquid by the body. When trying to cross a muddy puddle, the tank raises a huge wave and spray, which in most cases falls on its own armor. Considering that all this is happening at a solid speed, the consequences are sad and natural. It looks, of course, funny, at least in the photographs. However, not all so simple.
For a fighter, "catching a dolphin" is fraught with a visit to a bathhouse and washing clothes. But for the car, everything can end sadly. In rare cases, incorrect intersections of deep puddles can provoke an engine water hammer. But even if this does not happen, the dirt enters the inside of the tank through the open hatches. Dolphin catching happens only when the tank is marching. This means that its hatches are open, and the driver is leading the tank leaning out. After such incidents, tankers very often have to wash a significant part of the internal equipment from dirt.
Why did the tankers call this phenomenon that way? If you have ever seen dolphin performances, then everything should be clear at once. The dolphin jumps out of the water, flies over it, and then falls back into the water, creating a huge amount of splashes. Roughly the same thing happens with a tank when it flies into a deep mud puddle at speed. Hence the expression.
Continuing the topic, read for which Soviet tankers disliked the main tank of the USSR of World War II T-34 and not only.