18) In the soldier inventory screen, when an item is selected, press the keyboard shift key and click on a slot equips all the soldiers with the same item in the same slot, if the slot is free.
Also, right clicking on the soldier sprite unload all the soldier items, and press the keyboard shift key and right clicking on a soldier sprite unload all the items for all the soldiers (or/and add some buttons to the screen ;-) ).
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Cut from this thread on demand for better convenience:
https://openxcom.org/forum/index.php?topic=2279.0