By this time, Sperrle's boundary with Kesselring ran down the Sambre to Charleroi. Sperrle's job was to protect Guderian's southern flank, though he was ordered to assist against an attempted counter-attack near Arras by supporting the 4th Army advance north. Grauert's I. "Fliegerkorps" contributed to 300 sorties over Arras. Loerzer and Greim protected Guderian along the Aisne, the former supporting the 2nd and 12th armies. Sperrle's subordinates flew only seven operations against airfields from 20 to 23 May, but 54 against rail stations and another 47 against localities.