COIN is the military acronym for Counter Insurgency. Counter insurgency warfare has been, in a lot of ways, the main type of warfare we have been involved in since the end WWII. Certainly most of the Vietnam War, Iraq War, and the War in Afghanistan are counter insurgency campaigns.
Many of the tasks that I am going to discuss here can and have been accomplished by other aircraft. F-16s and F-18s are very good at hitting ground targets and carry weapons that can utterly destroy most anything. But they often can only stay above the battle for very short period of time, sometimes as little as 30 minutes. A savvy enemy can realize that if they lay low for a little while, the aircraft will have to leave the area to refuel. Aeriel refueling and stacking aircraft to come on station in sequence can help solve this problem. Advanced jets are also difficult or impossible to operate from small, primitive airfields, forcing commanders to fly them to their targets from further away.
Helicopters such as the AH-64 Apache and AH-1 Cobra are very useful in attacking ground targets, but also have limitations. They are in general much easier to shoot down than planes as they fly lower and are very much slower. They also may be unsuitable for certain types of time sensitive air support as they can't respond with the same speed as fixed wing craft.
Some of you might be thinking, man, this guy has completely forgotten about the best close air support plane in the air, the A-10 Thunderbolt II/ Warthog. No, I didn't. And the A-10 is probably the best close air support plane in our inventory (Sorry Harrier, you are cool too). But even the A-10 is not perfectly suited to supporting troops on the ground. The A-10 was mostly intended to destroy hordes of Soviet tanks on a open, plains-type environment.
The A-10 is in the process of being upgraded to allow it to use more precision weapons and that will increase its usefulness.
For an aircraft to be successful and useful in a counter insurgency situation, it must have a balance of several attributes.
1. Endurance: The aircraft must be able to loiter over the battlefield for extended periods of time to provide support for troops on the ground.
2. Slow speed maneuverability: To accurately hit small and camouflaged ground targets, the aircraft must be able to fly low and slow to be able to see. Higher speed aircraft like the F-16 have difficulty moving slow enough to spot targets like small bunkers, and even if they see them, they usually will have to come around for another pass, because they have flown a few thousand feet by the time they can recognize and confirm the target.
3. Survivability: Since the aircraft has to hang around a long time, flying low and slow, it is certainly going to receive ground fire from small arms, AA guns, rockets, and surface to air missiles. The aircraft has be designed to meet these threats as well as possible. Part of this is making the aircraft as tough as possible with extra armor for the pilots and redundant systems. Another is making sure the aircraft has systems like chaff and flares to increase its resistance to advance anti-air weapons.
So where does this leave us? What is the solution? Well, the simplest thing may be to buy and field more helicopter gunships, A-10s and even armed UAVs.
Another approach is to look backward. The US military has flown many excellent propeller driven aircraft in the past that would, with some modification, make excellent COIN aircraft.
Why propellers? Well, for starters, they are easier to operate in austere environments, they also are much harder to target with Infrared guided missiles as they do not generate anywhere near the heat of a jet engine.
This one is an outside possibility, but has a solid a combat record as can be wished.
This is the A-1 Skyraider, a plane designed for WWII that was so good, it was used all the way into Vietnam, well into the jet age. The Skyraider was very tough and had excellent low speed handling due to a large, low, straight wing. Notice the large speed brake beneath the fuselage. This allows the pilot to very quickly drop his airspeed, like letting the air out of a sail. That means they can approach a target quickly, slow down, bomb the crap out of it, and then throttle up and get out of there. While the A-1 is a wonderful plane and could be useful, it is extremely doubtful that the Pentagon would bring back a plane of this age.
Next up, the OV-1 Mohawk, a joint Marine/Army project from the Vietnam era. This was a light twin prop aircraft, designed for observation and reconnaissance as well as air strikes. It satisfies the requirements of a rugged plane, able to operate from small, unimproved fields. It also has a good loiter time and can be easily modified to accomplish different missions. The Mohawk was fitted with pods to drop supplies to troops from its under wing hardpoints. This is a wonderful addition, because sometimes a couple of hundred rounds and a few gallons of water can make the difference between life and death for besieged ground pounders. It has a side by side cockpit arrangement that increases the situational awareness of the pilots. The Mohawk was in inventory until the 1990's and was replaced by aircraft such as the DH-7 and the E-8 J-STARS. The OV-1 was primarily an aircraft dedicated to seeking out the enemy, rather than destroying it, and inter service squabbles between the Army and the Air Force doomed the further use of armed fixed wing planes for Army use. That is a shame, because there have been some in the Air Force that have been less than enthusiastic about flying the types of missions the Army needs them to, but they don't want the Army flying them either.
One of the best candidates is the OV-10 Bronco, another Vietnam era observation plane. It can loiter for up to three hours and was specifically designed for CAS and COIN. This aircraft was developed during the infancy of combat helicopters and was intended to be used for Forward Air Control (FAC). The Bronco was designed to be extremely versatile. It could take off from roads and fields, met the short takeoff and landing criteria of 800 feet, it could be launched from a aircraft carrier. The original specifications stated that it should be convertible to an amphibian, but I don't know it that ever panned out. It could be armed with 7.62mm machineguns, a 20mm cannon, Sidewinder missiles and carry 500 lb. bombs on its wings. With the second seat removed, it can carry 3,200 pounds of cargo, five paratroopers or two litter patients and an attendant. Normal operating fueled weight, with two crew was 9,910 lb. Maximum takeoff weight was 14,446 pounds.
One interesting feature is that the Bronco was originally developed to strafe weapons with self-loading recoilless rifles, which could deliver aimed explosive shells with less recoil than cannons, and a lower per-round weight than rockets. The airframe would thereby avoid the back blast. The Bronco performed observation, forward air control, helicopter escort, armed reconnaissance, gunfire spotting, utility light air transport and limited ground attack. The Bronco has also performed aerial radiological reconnaissance, tactical air observation, artillery and naval gunfire spotting and airborne control of tactical air support operations, and front line, low-level aerial photography.
A newer version of the Bronco, known as the OV-10X is under development by Boeing and it would feature the ability to use precision weapons, advanced sensors and avionics, but still retain the robust and simple construction of the original.
This is the Ayres Vigilante, a militarized version of the Thrush, which is the most popular agricultural plane ever. The government has several modified aircraft of this type that were used to destroy Colombian coco crops. These aircraft are a special anti-narcotics crop-spraying version of the Turbo-Thrush and were bought for for the US State Department. This version, known as the Narcotics Eradication Delivery System (NEDS) featured an armoured cockpit and engine to protect against hostile ground fire. Attempts were made to find military buyers in the mid eighties, but the Air Force was not interested.
My favorite of the bunch, this Piper PA-48 Enforcer. It is a more modern take on the greatest fighter of WWII, the P-51 Mustang. It has been fitted with wing mounted fuel tanks and what I believe is a spar for aerial refueling. Notice the 10 (!) under wing hardpoints. This would allow the Enforcer to carry a large and varied load of ordinance. It could easily be fitted with laser guided 70mm folding fin rockets, 250 and 500 pound bombs, etc. It also was tested with 6 .50 caliber machine guns, although a 20mm cannon or two would probably be more useful. Like the rest of the aircraft here, it is a robust plane, capable of operating almost anywhere.Unfortunately, the Air Force never showed much interest in the Enforcer, despite years of development and the best pedigree a prop plane could ask for. Only four were ever made.