Most modern fighters can attach drop tanks. Although they help increase the range of the aircraft, they also bring many limitations.
Combat aircraft, especially fighters, often have very powerful engines and consume a lot of fuel, so their range is limited. If you want to increase their flight range, you must give them more fuel. So the external fuel tank was born to solve the problem. They help the fighter fly further in bomber escort or base transfer missions, allowing it to reach targets further away from the airfield. In some cases, they also give aircraft more fuel to refuel allied aircraft in the air.
Because of such necessity, the auxiliary fuel tank appeared very early in the Spanish Civil War, became popular during World War II and is still fitted to most modern fighters today. Even all 5th generation stealth fighters such as the F-22 or Su-57 are equipped with it, regardless of this device causing the aircraft to lose its stealth ability.
The extra fuel tanks increase air resistance, reducing the aircraft’s speed. Their weight causes the aircraft to roll and rate of climb more slowly. They also increase the radar cross-section, making the aircraft more easily detected and locked from a distance. In addition, they also take up space on weapon hardpoints.
In short, the extra fuel tank helps to increase the aircraft’s range, but it reduces most of the flight characteristics, the ability to carry weapons and makes the aircraft easier to shoot down. So most of the extra fuel tanks on modern fighter jets are designed so that they can be removed when needed.
When entering air combat or under attack, fighter jets will often remove the extra fuel tanks, regardless of whether there is fuel left in them or not. In this way, the aircraft can regain its most flexible state to engage with the enemy, maneuver to dodge missiles or accelerate to retreat. To reduce waste, the fuel in the auxiliary tanks will be used first and then the fuel inside the aircraft.
An additional information, during the Vietnam War, American aircraft left the battlefield countless huge extra fuel tanks. So they become valuable materials for people to bring back to make pots and pans. Especially due to their elongated shape, optimized aerodynamics, these auxiliary fuel tanks are used as extremely good boats and canoes. They are both light, durable, and less resistant to water, and fuel efficient. If you come to Vietnam and see these boats, don’t be surprised.