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I asked two different military surveyors about aluminum survey pins.

The Cpl spoke from his experience on airfield survey jobs where the party's task was to accurately locate the centreline of semi-improved strips on military bases. The RCAF has a huge long checklist of quals for its tactical airlift pilots. One of them is to land and takeoff a C130 from a grass strip. To that end several bases have approved strips which are coincidentally exactly parallel with existing hard surface strips. There is one at Camp Wainwright for example. I flew into that one for (oh brother does this sound old!) for RV89.

The grubby military surveyor's job is therefore to locate both ends of a centreline to millimeter accuracy, so the bluejob with zippers everywhere can skid his shiny air-e-o-plane onto a GPS track in the mowed grass. Three checks in the box for his quals and a logbook entry for the record. Because grass strips are unimproved, the task only needed two markers that could be easily found again, wouldn't really matter if they got mowed over, or gradered out.

Despite the prevalence of good airfields all around the world, there are times when putting a C130 into an impossibly tight spot is necessary. Goofle search for JACMEL, HAITI. There is a grass strip there where the palm trees have encroached so much, the CF Herc' had to land sideways after the 2010 earthquake. JACMEL is also the hometown of Her Excellency the Governor General Michaelle Jean. Someone had to prove a point. (Your humble scribe was asked urgently by the Airfield Engineers at Air Force HQ, where is the nearest gravel pit so they could fill a few holes. Northwest and upstream about 3km, we see a borrow pit on the Haitian's own map sheet. Good luck Gravel Tech!)

The Warrant Officer for the Survey Troop had a similar response to his Cpl. An aluminum pin would be a temporary survey station, rather than a brass or iron pin to mark a permanent station. If the point needed to be revisited, the instrument man could find the pin and set his instrument exactly over top. Then he could resume a previously suspended job and take it to completion. Aluminum pins are expendable, but for a few months or a couple of years, they are intended to be used again. If left behind, shrug, no a big deal.