From my notes on the project at the time:
"Basically, they're all droids who had original functions that weren't directly related with combat. Either through reprogramming, or avoiding memory wipes long enough to develop distinct personalities, or even by accident, they all end up with combat based specialties. They're on the run, as most of their original owners want them back, and various corporations would like to figure out how they broke their programming. Corny as it may sound, they're like a droid version of the A-Team."
D3-M0 is the only member of the group that was created for military purposes. His original intention was to clear mines and explosives from a battlefield to clear the way for other troops. After time, the droid started to develop a taste for explosions, and by the time he joined up with the rest of the fugitive droids, he was an expert in demolitions.
D3-M0 was the first one I put together for the project, and was made from odds and ends I had left over from Gundams I used for other projects. His shape is loosely based on the "head-crabs" from Half-Life.