ALG code numbers. The stabilisation of the front lines in the Netherlands, Belgium, and eastern France in mid-September 1944, which would last into the new year, allowed aviation engineers a chance to reorganise and prepare for the upcoming winter season. As expected, they could not build new PHS and SMI airstrips during the fall rain and winter snow seasons because of the moist ground. Besides concrete, the American-made PSP was the only available surfacing material that could be laid down during this inclement weather in Europe. To keep the supply lines open, selected airfields in Belgium and France were therefore "winterized" with PSP. Because of the limited supply of PSP, however, only a limited number of airfields could be winterised, making it necessary to base two group sized units per airfield. But sufficient fighter-bomber and medium bomber airfields were completed that winter to ensure 2TAF and Ninth Air Force aircraft could continue flying combat missions. The major problem affecting airfield construction in early 1945 was not the surprise German Ardennes counteroffensive (which caused the abandonment of only one airfield – Y-39, Haguenau). Rather, an early February thaw threatened to make airfields inoperable due to the mud and water. Using local civilian labour, engineers performed extensive maintenance on the threatened airfields and successfully resolved the crisis. The renewed allied offensive in early 1945, following the Battle of the Bulge, was supported in earnest by the building of tactical airfields in occupied Germany. Trier (Y-57), became the first operational tactical American airfield on German soil on 10 March 1945. When a crossing over the Rhine River was spearheaded at Remagen, Germany, a supply and evacuation strip was quickly set up to support the bridgehead. As Allied tank columns struck out rapidly into the heartland of Germany, the airfield "clutches" of the Ninth Air Force's tactical air commands moved east of the Rhine river within range of virtually any target in Germany. Scores of former Luftwaffe sod and hard surfaced airfields were captured in the lightning advance through Central Germany, virtually undamaged, lessening the requirement for SMT, PHS, and PSP prefabricated surfacing. The relative lack of German military opposition in late March, April and May 1945 lessened the need for close air support and produced a greater demand for supply airstrips to keep the offensive moving. Every opportunity was used to clear captured German airfields for use along the armies' route, allowing C-47s