The IDF Rabbinate has paskened that IDF soldiers who are in combat must eat rather than fast this Friday. Soldiers in combat have to be battle fit, ready for any military ops at all times and cant be worn out, tired, sick, from fasting. 

The above applies to combat soldiers and equally to soldiers who are not yet in combat but could be sent into combat at any moment. Additionally, it applies to soldiers in other security roles including guard duty on various bases not on the front lines.

And additionally, the above applies to mechanics who must keep vehicles and planes ready and in combat shape - anybody who must be ready for physical activity for the war effort. 

The IDF Rabbinate explained further that anyone who needs to eat on the fast for combat reasons must eat regularly and normally without hiding the food from others. Anyone who must eat for combat purposes and then at some point during the day no longer needs to, should fast the rest of the day. 

Soldiers serving in non-combat roles but in combat support roles, such as in control rooms and other support roles should do their work on 10 Teves without eating but anyone who feels his functioning is slacking because of the fast should ask the rav of his unit to weigh the requirements and capabilities of any specific role and may be able to eat and drink. 

There are a lot of soldiers not in combat but waiting to be given orders. In the meantime they are hanging out in the staging areas near the Gaza border and active in training to prepare for possible entry. The IDF Rabbinate paskened for these soldiers to continue training as normal and as needed even if that means they wont be able to fast. 

source: Kipa, Srugim