Alongside the potential for gains in combat experience it is also thought that various strategic initiatives were first tried as part of Luftwaffe involvement in the conflict. Theories on strategic bombing were first developed by the Luftwaffe with the first exhibition of "carpet bombing" in the September 1937 Asturias campaign. Comparisons between the raid on Guernica and the fate of other cities during the conflict are also telling. As the fighting progressed into March 1938 Italian pilots flying as Aviazione Legionaria were involved in thirteen raids against Barcelona involving fire and gas bombs.