Using US National Grid System (USNG) GPS Coordinates on an iPhone - good luck with that

The boys and I are going mountain biking at the Cuyuna Trails near Ironton Minnesota. The map uses USNG - United States National Grid GPS coordinates.

For example: 2339-4834 is one coordinate. If we need emergency services we’re supposed to know where we are on the map and give them these coordinates. Way points on the map reference the coordinates.

I wondered — can I use these in my iPhone?

Unfortunately neither Apple nor Google Maps support USNG coordinate date entry. After some searching I found some suggested apps:

• Mobile App: a web app with an odd behavior — might be embedded javascript. They’re looking for someone to make it a real app. It seems to work — shows my current USNG coordinates. Might be a way to find where I am on the trail map.
• Apps | U.S. National Grid Information Center: 3rd party apps including Theodolite (iPad) and Pro Compass — that don’t actually seems to handle UNSG!

I also found “Map Tools”, but it is abandonware and has a nasty pricing scheme. (Incidentally, Apple App Store search is just atrocious.)

In the end the only app I could find that seemed to cover USNG and be well maintained was MilGPS. I bought it, though I’ll also test out “usngapp.org” — it does seem to work.

I wonder if USNG is either a dead end or a false start. (See also: 1-Introducing the United States National Grid.)

Update 7/1/2016

A comment mentioned the Gmap4 project. It is a pretty cool project, and the documentation has the best explanation of USNG I’ve found.

Gmap4 can dispay the USNG grid on Topo maps. Here is the Cuyuna area.

https://mappingsupport.com/p/gmap4.php?usng=15T_VM_2310_4883&tilt=off&z=14&t=t4

I am the developer of this enhanced Google map viewer. This is a public service and part of my way to 'pay it forward'.

This link and the USNG support works fine on cell phones and other mobile devices. For geolocation tap Menu ==> My location.

Gmap4 homepage: https://mappingsupport.com/p/gmap4.html

USNG support in Gmap4: https://mappingsupport.com/p/help_files/gmap4_usng_and_mgrs_coordinates.pdf