If you are referring to the highest altitude a military craft has gone, then it is Lockheed Martin U-2. It set the record for 70,000 feet.
Most military planes are not designed to operate at altitudes as high as 60,000 feet with troops onboard. While some specialized aircraft, like the U-2 reconnaissance plane, can fly at such altitudes, they are not equipped for troop transport. Generally, military transport aircraft operate at lower altitudes to ensure crew and passenger safety and comfort. Additionally, the lack of oxygen and extreme temperatures at 60,000 feet would pose significant risks to personnel without specialized equipment.
The altitude at which a plane can fly varies depending on the type of aircraft. Commercial airliners typically cruise at altitudes between 30,000 and 40,000 feet (about 9,000 to 12,000 meters). Smaller general aviation aircraft may fly at lower altitudes, generally below 25,000 feet. Military jets and specialized aircraft can reach altitudes exceeding 50,000 feet.
Zero, if the jet plane is on the ground, otherwise it depends at what altitude the plane happens to be flying. Cruising altitude for many passenger airliners is around five to seven miles. Military aircraft often fly at much higher altitudes.
Ventilation is important on a plane to compensate for air pressure as the plane is in a high altitudes and also to maintain suitable temperature and oxygen levels,
Well a simple answer would be that if a plane is not pressurized, on high altitudes or just very high in the sky, the plane will expand like a balloon and if it expands to much, big problems happen and I don't really know how it is pressurized but the air inside the plane is usually very different than the air outside the plane, at high altitudes.
Altitude sickness is caused by the body's inability to adjust to the lower oxygen levels at high altitudes. In a plane, the cabin is pressurized to simulate lower altitudes, so passengers can breathe comfortably without experiencing altitude sickness.
Depends which plane
A military plane is usually used whenever there is a military operation.
If you are sucked out of a plane during decompression, you would likely experience a sudden drop in air pressure and temperature, leading to rapid loss of consciousness due to hypoxia and asphyxiation. The extreme conditions at high altitudes would make survival highly unlikely.
Because they have winglets which cause them to release farts. These farts eventually cause the plane to explode.
The air is thicker at lower altitudes, we know that sound travels much better when it can move through solid mass. As you climb, the air starts to get thinner. It becomes much more difficult to do anything at high altitudes, including keeping a plane aloft, keeping warm, and of course projecting sound.
Better fuel economy. The air is thinner at higher altitudes.