By Keith A. Milks
Special to the [Marine Corps] Times

In the skies over Vietnam, amid fast-moving attack aircraft executing close-air support missions and helicopters ferrying troops in and out of remote jungle landing zones, an unobtrusive aircraft usually loitered in the background playing a key, yet understated role in that war.

Dubbed the Bird Dog, the O-1 series of aircraft was a common sight in Vietnam, and its pilots logged a staggering amount of hours flying the durable aircraft for the duration of the war. It was flown by Marine Corps, Army and Air Force pilots, as well as aviators with the New Zealand and South Vietnamese air forces, among others.

The Bird Dog was a militarized version of the Cessna C-170, and was designed to fulfill the Army's need for a standard liaison and observation aircraft. Production began for the Army in 1950 and the Marine Corps and Air Force ordered theirs soon after.

Upon entering military service, the C-170's designation was changed to L-19 and its cabin modified slightly to accommodate more radios. Unlike its single-seat civilian counterpart, the L-19 had space for two crewmen, the pilot and observer sitting fore and aft, respectively. In 1962, the aircraft underwent another name change and received its final designation as the O-1.

The O-1 was used in Korea and Vietnam. In both conflicts, it was primarily employed as a platform for battlefield observation and to control artillery fire and air-support direction.

Retired Master Sgt. Ed Alexander, who served with Marine Observer Squadron 6 in Vietnam and operates a Web site dedicated to it ( http://members.cox.net/hueyguns) , recalled that the '50s-era plane's radio-wiring harnesses became brittle with age and, when stepped on, would shatter.

"It would take about eight hours to rewire a UHF radio harness and then the aircraft would have to go on a maintenance test flight to make sure it got a 50-mile range test with the radios," he recalled in an Oct. 7 e-mail. After rewiring one of the Bird Dogs, Alexander, then a staff sergeant, told his lieutenant the plane was ready to go, and the two flew north out of Quang Tri for a test flight.

Ten or 15 minutes later, Alexander said, "we were on the north side of the DMZ taking pictures of NVA flags -- with no weapons aboard the plane. All the flights after that I let other Marines in the squadron fly, I told them to take their M-16s with them."

The primary differences in the Bird Dog's five variants were in the type of propeller system used and the aircraft's power plant. Early variants used a 210 horsepower Continental O-470-11 piston engine that later was upgraded to provide an output of 265 horsepower.

With a maximum speed of up to 130 miles per hour, the Bird Dog could cruise 530 miles. Most valuable to the infantry was the aircraft's on-station endurance and ability to loiter over a battlefield for up to five hours. Its ceiling was just over 5,600 meters, and climb rate was 1,150 feet per minute.

Rugged and compact, the Bird Dog could operate from even the most remote airstrips, which usually were carved out of the jungle. Weighing in at 1,600 pounds, the aircraft had a wingspan of 36 feet, was 26 feet long and stood a mere 7 feet, 4 inches tall.

The Bird Dog could carry various payloads on four pylons under its wings. Usually, the aircraft was outfitted with 2.75-inch white-phosphorus marking rockets to highlight the precise location where attack aircraft were to drop munitions or where helicopters should land.

For night missions, the pylons could be outfitted with 2-million candlepower flares to provide illumination for ground operations. Though not designed to engage in combat and no official record exists of any armament carried on the aircraft beyond personal weapons, a photo on USMC Vietnam Helicopter Association Web site, located at https://www.popasmoke.com/visions/image.php?source=3453 , shows an unidentified ordnanceman arming rockets on a VMO-6 Bird Dog.

"The O-1 pilots in Vietnam were the most decorated of any pilots and had the most causalities," recalled Robert J. Moriarty, a captain when he flew the Bird Dog with VMO-6 in Vietnam in 1968-69. At least two pilots he knew earned the Silver Star for their actions, he said, and nearly every O-1 pilot received at least one Distinguished Flying Cross.

"The O-1 was the slowest aircraft in the Marine inventory, flew the lowest, drew the most fire and was by far the deadliest plane we used," Moriarty said.

Although the Bird Dog was less glamorous than attack helicopters or fighter jets, pilots were renowned for their allegiance to the little plane and for their contribution to the war. The O-1 remained in service for several years after Vietnam and still can be seen in frontline service in countries throughout the world.