If I were lost in rural Honduras and the US marines were gracious
enough to come pluck me out, would the helicopter pilot prefer to know
my location in long/lat or in UTM?  I understand they are easily
convertable to one another, but which is the linga franca of pilots
and military folk?

Howdy defaultuser-ga,

The Marines would actually like your coordinates in yet a different method,
that being the "Military Grid Reference System" or MGRS.  In worse case, as
MGRS is based on "Universal Transverse Mercator" or UTM, that would do in a
pinch.  This "doc" file located on an official U.S. Navy web site goes into
some detail.

"Military Map Reading 201"
https://www.navigator.navy.mil/navigator/map_reading_201.doc

"This information paper is designed to resolve the confusion between the
Universal Transverse Mercator (UTM) and the Military Grid Reference System
(MGRS) coordinates.  The two systems are often used interchangeably, but
they are not the same. Most of our allies, intelligence databases, and many
software packages use the UTM system.  The Army and Marine Corps proposed
the MGRS convention to simplify coordinate exchange for the soldier/marine
in the field.  The aim of this paper is for users to understand both the UTM
and MGRS systems and be able pull coordinates on multiple scales of maps and
charts.
...
The MGRS system was designed to simplify the specification of position and
passing of coordinates for soldiers and marines.  The MGRS system allows
users to abbreviate the 13-digit UTM coordinate, making it easier to use."

You should read the above referenced article in detail to learn on how to
convert UTM to MGRS, at least the next time you are heading to Honduras.

If you need any clarification, please feel free to ask.


Search strategy:

Google search on: "The Marines" navigation training UTM
://www.google.com/search?q=%22The+Marines%22+navigation+training+UTM

Google search on: Marines "Military Grid Reference System" MGRS
://www.google.com/search?q=Marines+%22Military+Grid+Reference+System%22+MGRS

Looking Forward, denco-ga - Google Answers Researcher

Gracias de Honduras a zonk22, tambien.

Aviation maps with scales of 250,000:1 have both for margin
information provide as do all military maps.  UTM makes more 'grid'
sense in order to find you.  The GPS equipment can go either way
though.  Personaly, I'd call the Army to help me but I'm bias...oh,
and  don't get lost easily.

Thanks for the 5 star rating and generous tip, defaultuser-ga.

Looking Forward, denco-ga - Google Answers Researcher