In the late 1960s, the U.S. Air Force gave up on a plan to transform old sub-hunting planes into attack aircraft. But the Navy actually did send modified P-2 Neptune patrol aircraft to fight in Southeast Asia.

In 1967, the first batch of converted sub-chasers arrived in Thailand for a secret mission. The 12 planes—called OP-2Es, one of which is seen in storage above—were meant to drop special sensors that could track the enemy’s every movement.

The Pentagon hoped these sensors would help break up North Vietnam’s complex network of roads and trails in Laos—a.k.a., the Ho Chi Minh Trail. The Navy and Air Force couldn’t attack an enemy they couldn’t find in the first place.

The special four-engined planes dropped devices that looked like camouflaged sonar buoys—normally used to track submarines—or giant lawn darts. Engineers designers these sensors to get snagged in the trees or to bury themselves in the jungle floor.

Analysts back in Thailand would activate the microphones and listen in for the enemy. Some of the sensors could detect the ground shaking as trucks—or some unfortunate water buffalo—trundled by.

The Acoubuoy, seen at left, had microphones to listen for the enemy. The Air-Delivered Seismic Intrusion Detector — or ADSID, depicted on the right — could ‘feel’ trucks drive by. Air Force photos

The low and slow flying Neptunes only had to toss the special equipment onto the trail. American commanders would then call in fighter jets and bombers to attack the convoys.

But the missions were hardly a cakewalk. The pilots and crews of Observation Squadron 67 regularly squared off against North Vietnamese anti-aircraft guns.

The aircraft had dispensers in the tail full of a small strips of metal called chaff. This countermeasure could blind hostile radars, but did nothing to stop the murderous fire from 23- and 57-millimeter cannons on the ground.

The planes could only respond with their token armament—two rapid-firing Miniguns under the wings. Two other machine guns stuck out of the aircraft’s rear emergency exist windows like you see on a World War II bomber.

An OP-2E’s best option was to avoid fights whenever possible. By March 1968, three of the Neptunes had been shot down and 20 Navy fliers had died.

Three months later, the planes departed Southeast Asia for good and their war service came to a close. The military rigged up fast-flying F-4 jets to drop the sensors, instead.

The aircrews swore to secrecy and the Pentagon waited until 1998 to acknowledge the mission, according to the VO-67 alumni association.

The AP-2H could carry bombs, napalm, rockets and machine guns under its wings. The aircraft also had rear guns like the OP-2E variants.

In addition, at least one AP-2H also kept a nasty surprise in its bomb bay, according to a Website maintained by former pilots and crew. Eight 40-millimeter grenade launchers hid inside, pointing downward at various angles.

These guns fired through holes in the bomb bay doors. The weapons could spray high-explosive shells over an area the size of a football field, as long as the pilot flew at the correct altitude.

The Navy’s new gunships soon were flying missions over the Mekong Delta region in both South Vietnam and Cambodia. The special planes also blew up trucks in Laos.

Unlike VO-67, Heavy Attack Squadron 21 suffered no casualties during its tour of duty and all of its aircraft survived the fighting. But the military still considered the old propeller-driven planes to be too vulnerable.

In 1969, the AP-2Hs followed the OP-2Es out of the region and into storage. The following year, a batch of specially modified A-6C Intruder jets arrived to take over the same missions.

You can follow Joe Trevithick on Twitter at @FranticGoat. Sign up for a daily War is Boring email update here. Subscribe to WIB’s RSS feed here and follow the main page here.

War Is Boring

From drones to AKs, high technology to low politics, exploring how and why we fight above, on and below an angry world

    War Is Boring

    Written by

    We go to war so you don’t have to

    War Is Boring

    From drones to AKs, high technology to low politics, exploring how and why we fight above, on and below an angry world

    Welcome to a place where words matter. On Medium, smart voices and original ideas take center stage - with no ads in sight. Watch
    Follow all the topics you care about, and we’ll deliver the best stories for you to your homepage and inbox. Explore
    Get unlimited access to the best stories on Medium — and support writers while you’re at it. Just $5/month. Upgrade