Question: Operation "Greif" was a special operation during a battle where which forces incurred their  highest casualties of any operation during the war ?

Operation "Greif" (German: "Unternehmen Greif" ; ] , meaning "Griffin") was a special operation commanded by Waffen-SS commando Otto Skorzeny during the Battle of the Bulge in World War II.  The operation was the brainchild of Adolf Hitler, and its purpose was to capture one or more of the bridges over the Meuse river before they could be destroyed.  German soldiers, wearing captured British and US Army uniforms and using captured Allied vehicles, were to cause confusion in the rear of the Allied lines.  A lack of vehicles, uniforms, and equipment limited the operation and it never achieved its original aim of securing the Meuse bridges.  Skorzeny's postwar trial set a precedent clarifying article 4 of the Geneva Convention: as the German soldiers removed the Allied uniforms before engaging in combat, they were not to be considered francs-tireurs. <SEP> The Battle of the Bulge (16 December 1944 – 25 January 1945) was the last major German offensive campaign on the Western Front during World War II.  American forces bore the brunt of the attack and incurred their highest casualties of any operation during the war.  It was launched through the densely forested Ardennes region of Wallonia in eastern Belgium, northeast France, and Luxembourg, towards the end of World War II.  The surprise attack caught the Allied forces completely off guard.  The battle also severely depleted Germany's armored forces, and they were largely unable to replace them.  German personnel and, later, Luftwaffe aircraft (in the concluding stages of the engagement) also sustained heavy losses. <SEP> The Battle of Suoi Bong Trang (23–24 February 1966) was an engagement fought between US, Australian and New Zealand forces, and the Viet Cong and North Vietnamese Army during the Vietnam War.  The battle occurred during Operation Rolling Stone, an American security operation to protect engineers building a tactically important road in the vicinity of Tan Binh, in central Binh Duong Province, 30 km north-west of Bien Hoa airbase.  During the fighting, soldiers from the US 1st Brigade, 1st Infantry Division and the 1st Battalion, Royal Australian Regiment (1 RAR), which had been attached for the operation, fought off a regimental-sized Viet Cong night assault.  Repulsed by massed firepower from artillery and tanks, the Viet Cong suffered heavy casualties and were forced to withdraw by morning.  After the attack, the Americans and Australians made no attempt to pursue the Viet Cong, focusing on securing the battlefield and evacuating their own casualties.  The Viet Cong continued to harass the American sappers with occasional sniper and mortar fire, but these tactics proved ineffective, and the road was completed by 2 March. <SEP> The Battle of Go Cong was a small battle during the Vietnam War.  It took place on September 3, 1963, after the General Staff of the Viet Cong (NLF) called for "another Ap Bac" on South Vietnamese forces.  The intent of the operation was to drive out the rebels who had survived the earlier Ap Bac engagement.  The battle was won by American and South Vietnamese forces, after inflicting heavy casualties on the Viet Cong, using artillery to slaughter rebel fighters fleeing American special operation troops who ambushed them with intense sniper fire.  It was later discovered that the 91 of the captured NLF troops were new recruits, and did not have weapons.