QinetiQ built a hybrid off-road truck demonstrator a bit like an Alvis Stalwart. Claimed advantages were simpler transmission (a motor in each wheel), and reduced thermal and noise signatures. Short range movements could be made on batteries alone, with claimed reduced risk of detection.
https://www.qinetiq.com/news/2016/08...rpa-investment
The Navy has had electric vehicles, AKA submarines, for over a century, and now electric surface vessels in the shape of Type 45 destroyers, although the latter do seem to have got off to a bit of an inauspicious start.
Aircraft-wise, Desert Hawk and in the near future, Zephyr are the trend setters.