Twin tails AKA H-tails have some general advantages and disadvantages, and some advantages specific to multi-engine planes and military aircraft.

1. Having two rudders gives the same control surface area in a less-tall package. A single rudder will need to be taller, and being on top of the tail section of the fuselage, rather than beside it as possible with twin tails, adds to the height. For large aircraft, this can make them impossible to fit in existing hangers.

2. Moving the rudders away from the airflow that is disturbed by the fuselage helps them work better.

For a multi-engine aircraft,

• Low-speed response of the rudders can be improved by putting them in the airflow from the engines. This makes the air flow speed over the rudders greater than the airspeed of the aircraft, which can improve the low-speed effectiveness of the rudder.

Two further advantage that are more specific to military use are:

1. A twin tail provides a clearer field of fire directly backward for a dorsal gunner. For large bombers with tail gunners, this means that both the tail gunner and dorsal gunner can engage fighters approaching from behind. For aircraft with a dorsal gunner but no tail gunner, such as, e.g., the Messerschmitt Bf110, this is even more important - while 2 gunners being able to engage an attacker is better than 1, 1 is even more better than zero.

2. The redundancy of a second rudder means that some control is still available (even if less effective) if one rudder is destroyed by enemy fire.

There are some disadvantages:

1. It's more complicated - control cables need to control two rudders rather than one.

2. For the same frontal area of rudder, there is more drag.

3. The tail can be more susceptible to flutter at lower speeds. "Flutter" is when the aerodynamic forces on part of the aircraft make it oscillate too much.

4. If the boost to performance from being in the higher-speed airflow from the engines is exploited to make the rudders smaller, the rudder on one side can fail if the engines on that side fail.

Twin tail fighter aircraft are common today, while many other twin tail aircraft that still fly are old designs, many dating to the 1930s. There are some more modern twin-tail subsonic aircraft in use, such as the Fairchild Republic A-10 Thunderbolt II (a US ground-attack aircraft), the Harbin SH-5 (a Chinese maritime patrol aircraft), and multiple Antonov transport aircraft. The Northrop Grumman E-2 Hawkeye (a US carrier-based airborne early warning (AEW) aircraft) should also be mentioned, even if it is a quad tail rather than a twin tail.