With victories at Hockenheim, the Schauinsland Hillclimb, and the Grenzlandring, Ulmen was clear champion in the 2-litre Sports Car class. He participated in two World Championship Grands Prix in 1952, debuting on 18 May 1952, in the Großer Pries der Schweiz, but retired due to fuel tank issues. He returned for the Großer Preis von Deutschland, where despite his Veritas's power disadvantage compared to his rivals, his finished eighth. That season also saw Ulmen win the DMV Grenalandringrennen again. During the season, he suffered a heavy crash during a practise session on the Sachsenring from which he escaped almost unscathed. He arrived at the final meeting of the 1952 season, the Avusrennen, as leader in the Formula 2 class and 2-litre sport cars. On the AVUS, lost a dramatic slipstream battle with fellow Veritas driver, Fritz Rieß, on the penultimate lap. This meant both drivers were equal on points, and according to the DMV regulations, Rieß was declared champion, as he had scored the better at the Eifelrennen. As consolidation, Ulmen was awarded the Formula 2 title, despite the fact he could take part in this race. After that he competed only occasionally in car races.