#grossmesser

I think – and this is just IMO – that theywere mostly used in everyday clothes…

…or against mostly-unarmoured battlefieldopponents like Landsknechts, since anti-armour weapons of the period (exceptfor polearms like bills etc.) tended to rely less on cutting than stabbing atweak spots (half-sword with longswords, spikes on pollaxes) or bludgeoning forblunt-force trauma without penetrating the armour (mordschlag with longsword,maces/war-hammers.) 

While one of the various names for the bighand-and-half versions is Kriegsmesser (war knife), suggesting military use,I’m not sure whether that’s a contemporary 15th-16th century word or somethingmade up by later historians. AFAIK (which isn’t as much as it should be by a long chalk) the word used in period fight manuals isjust Messer.

Speaking of Fechtbucher, Talhoffer has twosections devoted to fighting with the longsword (in everyday clothing and in full plate) butthe illustrations for the Messer section shows only unarmoured men, the Messersare the single-handed versions, and the opening stance ofthe combatants is quite stylised, with left hand tucked behind the back.

Of course once the grappling started, all that stylised formality went right out of the window.

There are a few instances in other manuals showing bucklers...

including this spiked “Hungarian shield“ which looks like a small version of the spike-and-hook shield in Talhoffer’s section on judicial combat...

…but otherwise no armour, not even mail. If there were specialisedtechniques more safely performed in armour with gauntlets than bare-handed in adoublet, I have a feeling they would have been included. (Of course this may simply mean I haven’t seen the manuals that include them, so next comment requires a pinch of salt...)

The lack of such techniques suggests (to me, anyway) that Messers of any size were intended more forunarmoured use - though as mentioned in connection with Landsknechts, that doesn’t mean purely civilian use.