The following picture shows the scene of the Polish Army Mechanized Brigade conducting tank diving training. A K2PL main battle tank has entered the river, with rolling waves submerging its body and its high gun barrels exposed to the water. There is a three-stage straight barrel standing behind the barrel, and the commander is observing the tank's movement after entering the water. When necessary, he can command the driver in the car to operate underwater through the intercom. On the distant shore, another K2PL main battle tank is ready and ready for diving at any time. There is also a tank rescue vehicle on the nearby riverbank, ready to respond to any unexpected situations in the river at any time. Tank armored vehicles can navigate through relatively narrow water barriers by floating or diving. Submarine crossing refers to the complete submergence of tanks and armored vehicles into the water, using sealing measures and submersible equipment to pass through the bottom of the water. On the other hand, a floating ferry is like a boat sailing over the water surface. Generally speaking, light armored vehicles such as amphibious tanks and infantry fighting vehicles use a floating crossing method to cross the river, while heavy main battle tanks can only cross the river by diving. Moreover, tanks need to undergo a complex 'preparation' before diving. Choose a diving site. The entry and exit points of tank armored vehicles are generally selected in areas with gentle river slopes, and the depth and velocity of the river water are surveyed in advance. Generally speaking, the depth of the river in the tank diving area should not exceed 4 meters, the flow rate of the river should not exceed 2 meters per second, and the bottom of the water should be as flat, hard, and free of large obstacles as possible to ensure smooth passage. After selecting the diving site, it is necessary to seal the tank. Modern tanks generally have the "three defenses" function, and the body has good air tightness. Generally, sealing oil is applied to the gaps and sealing airbags are installed at large gaps. In addition, due to the inability of the engine to dissipate heat properly after the tank is sealed, the engine water temperature rises rapidly, so it is necessary to complete the diving before the engine "boils". Usually, the diving distance does not exceed 800 meters and the diving time does not exceed half an hour. Finally, it is necessary to install ventilation pipes for the tank. The ventilation pipe is generally made of a metal tube with a diameter of 15 to 20 centimeters and a length of 4 meters, and is installed on the connecting seat ring of the vehicle commander or loading hand compartment cover above the turret. Air enters the cabin through the ventilation pipe for use by passengers and the engine inside the vehicle. The K2PL main battle tank in the picture is equipped with a thicker ventilation pipe, which can also serve as an escape route for passengers in emergency situations. After completing the above preparations, the crew put on their life-saving equipment and entered the tank to begin diving. During the diving process, the engine keeps running at high speed until the tank comes ashore. After landing, the crew will quickly dismantle the submersible equipment to restore the tank to normal driving condition. Diving has important tactical and even strategic value. During wartime, in areas with dense water networks, the pontoon bridge troops were unable to set up floating bridges on every river in a timely manner, requiring tank ferries to pass through. It is worth noting that outdoor diving has certain risks. The underwater conditions in wild waters are complex, and the silt may be too thick for the tracks to grip; It is also possible that there are large rocks, pits, etc. underwater, and tanks may not be able to come out after entering. Tanks undergo diving training to cope with various situations. (New Society)