In the Portland, Oregon, metropolitan area, where the Redhawks of the 123rd Fighter Squadron fly today, if someone says “Tri-Met,” most local folks will immediately think of the bus, light rail and commuter rail forms of public transportation in the Portland Metro area.

But long before this Tri-Met, in the skies over Southeast Asia, the Redhawks of the 123rd, when they were designated as the 35th Photo Recon Squadron, used another kind of Trimet to get their work done…

Trimetrogon, actually, is the more proper term, for a system of aerial photo mapping using three cameras, a vertical and two oblique (one left side and one right side) taking photographs simultaneously.

Three aerial cameras in Trimetrogon configuration.

Three aerial cameras in Trimetrogon configuration.

This Trimetrogon system of photogrammetric compilation, developed by the US Geological Survey for reconnaissance purposes in World War II, was an asset that proved invaluable to creating maps used by military forces.  There was a great need for this capability during the global conflict, given the vast expanses of uncharted or poorly mapped geographic areas around the world, such as the 35PRS was faced with in Southeast Asia in 1944-45.

In fact, in addition to the photo lab section and photo interpreters who printed and exploited aerial photographs, the 35PRS had a Photogrammetry Section of some 40 men in order to create maps from Trimetrogon-derived photographs.  When the squadron arrived at Kunming, China in September, 1944, it lingered there a few days before moving on to Chanyi Airfield.  But the Photogrammetry Section remained at Kunming, perhaps because 14th Air Force headquarters decided to keep it there.  It wasn’t until February, 1945, as noted in the 35PRS history for that month, that the section was actually formally transferred from the squadron to Kunming:  “On 6 Feb, 40 enlisted men comprising the photogrammatic section were transferred to the 4th Photo Tech Squadron upon activation of that unit.”

Mr. H. Allen Larsen was a veteran of the 35PRS Photogrammetry Section.  He recalled some of that experience in a telephone conversation on 19 February 2014.

H. Allen Larsen of the 35th PRS Photogrammetry Section poses in front of a P-40 fighter at Kunming, China.

H. Allen Larsen of the 35th PRS Photogrammetry Section poses in front of a P-40 fighter at Kunming, China.

He remembered an F-5 Photo Lightning pilot who flew a Trimet mission over Hainan Island, off the coast of China, but one of the oblique cameras failed.  After the mission, he asked the men in the photogrammetry section whether they still could perform their work without the aerial photographs from the malfunctioning camera.  No, they couldn’t, was the answer, they needed all three images.  The pilot, disappointed but undaunted, went and flew the mission again to obtain the required pictures.   Of note, Mr. Larsen’s book of wartime photographs, “China in the Eyes of Flying Tiger,” was recently published in both Chinese and English languages.

Cover of H. Allen Larsen and William L. Dibble's "China in the Eyes of Flying Tigers."

Cover of H. Allen Larsen and William L. Dibble’s “China in the Eyes of Flying Tigers.” You can see the 35PRS emblem on the jacket of the Airman with a pipe.

You can read about this wonderful work at:

So it was there at Kunming, where members of the 35PRS Photogrammetry Section performed an essential service for the Allied forces in the China-Burma-India Theater, mapping many areas of Southeast Asia, ranging from China to (then) Indo-China, Thailand and Burma.  The section utilized Trimetrogon-derived aerial photographs from both the 35PRS and the Kunming-based 21st Photo Recon Squadron.  One could thus say that with “Trimet,” these members of the 35PRS helped defeat fascism and militarism during the Second World War.


“The Geodet” article posting in blog Aggregat, dated 8 Jul 2006, at:

“F-5 Lightning Development,” article on 34 Photo Recon Squadron website, at: