Sig Sauer M-37 “Weasel” 10mm Caseless Pistol

M-37 Weasel 9x21mm Pistol 3

ROBOTECH Technical Files

by Tim Wing, Pieter Thomassen, with Peter Walker, Chris Meadows and Robert Morgenstern


Designation: Sig Sauer M-37 “Weasel” 10mm Caseless Pistol

  • Year Introduced: 2020
  • Designer: Sig Sauer
  • Acquiring Military: REF, UEDF
  • Capacity: 15 round magazine (typical)
  • Rate of Fire: semi-automatic
  • Weight: 1.6 kg (loaded, M-37), 1.1 kg (loaded, M-37A2)
  • Length: 20cm

Though the UN Spacy had adopted the ancient venerable Browning Hi Power back in the early 2000’s, after the consolidation of the different militaries of the Unified Forces in 2017, the newly formed UEDF found itself with an absolute multitude of different military pistols. These pistols ran the gamut from modern Glock 17s to the ridiculously antiquated M1911s of the US military. The UEDF decided that a single pistol design should be adopted to replace this mish-mash of firearms. After coming to this decision, the UEDF proceeded to adopted no fewer than nine different conventional and directed energy pistols in the same number of years.

M-37 Weasel 9x21mm Pistol 10The first pistol to be adopted was the Sig Sauer M-37. Based upon the Sig Sauer P420 series pistols of the late twentieth-century, M-37 introduced the 10mm caseless round. This weapon became (and remains to this day) the standard conventional police and security pistol for military and civilian use alike, outliving many of the other pistol designs adopted by the UEDF. The M-37 was also adopted by the Reconnaissance Expeditionary Force (REF) and remained in service with them even after the introduction of the SAL-9 and H-90 energy pistols.

Aside from its use of the new 10mm caseless ammunition, the M-37 was a conventional recoil operated pistol with a double-action/single-action (DA/SA) trigger mechanism. The 10mm caseless round came in both conventional ball and expanding hollow-point ammunition, as well as High Explosive Armor Piercing (HEAP) ammunition. The M-37 had Sig Sauer’s standard de-cocking lever, but featured a controversial safety selector. The safety was shaped like a dial that proved to be hard to manipulate under combat conditions. This really was not such a big hindrance though, as the pistol could be manually de-cocked and carried with the hammer down while and a round in the chamber. Rather than being made from composite materials like most of its competitors, the M-37 feature all metal construction of extremely corrosion-resistant alloys. This resulted in an excessively heavy weight of 1,600 grams when loaded (for reference an M1911 weighed in at 1,360 grams loaded). The heavy weight of the pistol was primarily to deal with the high chamber pressures created by the HEAP round. This was reduced in later models to a more manageable weight of 900 grams empty through the use of newer alloys and a ceramic barrel. The P420/M-37 is widely considered to be the pinnacle of traditional automatic pistol design and continues to be a popular sidearm to this day, over fifty years after it was introduced.

M-37 Weasel 9x21mm Pistol 8


Robotech (R) is the property of Harmony Gold. Super Dimension Cavalry Southern Cross (R) is the property of Big West Advertising, Tatsunoko Studio and Ammonite studio. This document is in no way intended to infringe upon their rights.

Original artwork by: Kogawa Tomonori, Hiroyuki Kitazume, Miyo Sonoda, Hiroshi Ogawa, Hirotoshi Ohkura and Takashi Ono

Acknowledgement is extended to Peter Walker, Pieter Thomassen and Robert Morgenstern of the unofficial Robotech Reference Guide. Peter Walker, Pieter Thomassen and Robert Morgenstern are given credit for all quotes and paraphrasing of the unofficial Robotech Reference Guide that has been utilized in this publication. 

Images from – This is Animation #10 The Southern Cross, Unspecified Super Dimension Cavalry Southern Cross OSM, Robotech II: The RPG, The Sentinels (September 1988)

Content by Tim Wing, Peter Walker and Pieter Thomassen, with Chris Meadows and Rob Morgenstern

Copyright © 2006, 1997 Robert Morgenstern, Pieter Thomassen, Peter Walker; 2016 Tim Wing