On the Allied side the first operational use of a helicopter was 1Lt Carter Harman of the 1st Air Commando Group flying a Sikorsky YR-4 from 21st April 1944, rescuing the pilot and passengers of a downed light aircraft. The mission rather illustrates the limitations of range and power of Sikorsky's first helicopters, particularly in the heat of Burma; Harman had to fly in stages to a temporary airstrip, then ferry the pilot and casualties one by one from the crash site. 1st Air Commando Group: Any Place, Any Time, Anywhere by Major R. D. Van Wagner says that 23 helicopter sorties were flown in total, but the YR-4 returned to India on 4th May and was withdrawn after the engine failed. It had a minimal effect on Operation Thursday compared to the L-1 and L-5 light aircraft of the 1st ACG and was more of a proof-of-concept really.

Helicopter have effected nearly every area of military operations from logistics, transportation, medical evacuations, command and control, ISR (Intelligence, surveillance and reconnaissance), and attack. The have given militaries with large Heli borne forces a force multiplier nearly akin to that of fully mechanized militaries.

Medevac (Or Medivac) began in Burma and by the Korean War use of H-19 for medivacs became relatively common as method of transporting wounded UN troops to MASH locations from causality collection points as they could fly over the rough terrain faster than ground transportation could by road. (Spurgeon H. Neel, Jr., Lt. Col., MC, "Medical Considerations in Helicopter Evacuation," U.S. Armed Forces Medical Journal, Volume V, No. 2 February 1954). This method become nearly ubiquitous during the Vietnam War as the distance and terrain made it difficult and time consuming for other modes of transportation. This trend continues to today for both military and civilian populations as a method of saving patients by reducing time between traumatic injury/wounds to being seen by advance medical care (the golden hour concept). Texas Tech as a very accessible online resource catalog on Medevacs during ‘Nam. (http://www.vietnam.ttu.edu/resources/dustoff/)

Logistics and transportation of troops was altered great by the speed and coverage helios especially over unforgiving terrain and urban environments offered compared to ground vehicles. CH-47 Chinook introduced in 1962 is still one of the fastest helicopters in the air with a max speed of 170 knots, range of 400 nmi (combat range 200 nmi) and can carry up to 24,000 lb or a platoon of fully equipped men (http://www.boeing.com/assets/pdf/rotorcraft/military/ch47d/docs/CH-47F_overview.pdf).

The ability to in essence to ignore most terrain (you still have a maximum altitude/ service ceiling to deal with, which is of particular concern in places like Afghanistan were the helicopters ceiling is still below some mountain tops). Bypassing rivers, forests, hills, etc combined high speed enables air assault forces flexibility both strategically and tactically over strictly ground based units. The shock factor involved by the speed that a force can descend upon their opponent or flank them via a previously secure avenue is not a minor advantage.

During the 1950s helicopters would start being armed thus birthing the attack helicopter role, modifying exist choppers to having rocket pods, etc. The AH-1 was the first true attack helicopter to be built in 1965, with Soviet response being the Mi-24 an attack choppers with transportation capabilities in 1969. The creation of attack helicopters allowed for a more mobile force to have fire support in another form and in rough terrain where tanks or IFVs are unable to reach, an invaluable support.

All of that said they are still highly vulnerable to enemy ground fire ranging from smaller arms, heavy machine guns, MANPADs, AA guns, and other missile system. The US Army had a reminder of this during the 2003 invasion of Iraq at Karbala where out of 31 Apaches (arguably the best attack helicopter on the planet) 1 was shot down one crash, and the rest were damages two enough where that would be their final flight (Atkinson, Rick. In the Company of Soldiers. Paw Prints. 2008.)