First, the 26th Iinfantry Division probably has a chronical of it's exploits that was written at the end of the war. These combat chronicals identify who did what down to the regimental level but, not any lower. Regiments are made up of battalions and battalions are made up of companies so, there are numerous Company F's. In WWII infantry divisions had 3 infantry regiments in their table of organization. If you can come up with your father's regiment you should be able to get an approximate idea of what he was involved in. The personell files of soldiers are available from the National Archives branch in St. Louis but, they had a fire in 1973 and a lot of stuff was destroyed. Most folks make a request on the off chance that what they are after has survived. One of the sources that can be searched in lieu of the actual personnel file is a soldier's records with the Veteran's Administration. Particularly if the veteran had in-service injuries that required treatment at a VA hospital.