duck duck go gave me the following:
THE NAME "TIP OF THE SPEAR" REFERS TO SOLDIERS, MARINES, AIRMEN, SAILORS AND COAST GUARD PERSONNEL WHO ARE IN HARM'S WAY AT THE VERY FRONT LINES, OFTEN IN DIRECT CONFRONTATION WITH AMERICA'S ENEMIES. Right now, the "Tip of the spear" is typically a remote outpost in rural Afghanistan and the Middle East.