The temporary victory ended in February 1944 with Big Week, part of Operation Argument. The American-led operation was a series of attacks against German fighter production. All three "gruppen" were involved in the defensive effort. By 25 February, the strength of II. and III. "Gruppen" were so low that they were ordered to parallel the bomber stream and attack only unescorted bombers on that day. I. "Gruppe", the strongest in JG 26, did succeed in downing four B-26 Marauder medium bombers which accompanied every mission. The American operations were successful, if overstated in the damage done to German production, but air superiority in daylight had passed irrevocably to the Allies. This month had seen the introduction into the air war of the North American P-51 Mustang. The fighter eventually had the range and performance to escort US bombers to the target and back which supplemented the drop-tank fitted P-47s and P-38s. American tactics soon changed from protecting the US bombers to patrolling fixed boxes of airspace. American fighter pilots were free to hunt German fighters; bombers that missed their rendezvous were left to fend for themselves. This marked a more aggressive use of VIII Fighter Command. The RAF 2nd Tactical Air Force was also released from escort duty—the Spitfires were now authorised to seek out the Luftwaffe while the bombers softened up the invasion coast in preparation for Operation Overlord. JG 26 was credited with 56 Allied aircraft in January but lost 19 killed and six wounded. 45 were credited in February for 18 killed and 17 wounded. On 6 March the Americans attacked Berlin; JG 26 claimed seven American and one British aircraft in combat with the main and diversionary forces for one loss. Two days later the Americans struck again; III. "Gruppe" reached the bombers but were engaged by US fighters. Two pilots were killed and one wounded against the P-47s. JG 26 pilots were given credit for nine American aircraft. On 16 March this "gruppe" attempted to intercept returning US bombers over France but the coordinated action with JG 2 failed. Three bombers were claimed but lost five killed and four wounded. On 31 March, the Eighth was placed under Dwight D Eisenhower's command for the invasion and the Combined Bomber Offensive was suspended.