As a lieutenant D?eln took part in Gustav III's Russian War and was wounded in the head in at the Battle of Porrassalami. The wound didn't heal and he was forced to wear a band around his head for the rest of his life.
After this he rapidly advanced to colonel and took part in the Finnish War. On September 13 1808 he lead the Swedish troops in the Battle of Jutas. For this he would become legendary after Johan Ludvig Runeberg wrote his epic poem D?eln at Jutas.
In the Second War against Napoleon he lead troops in Swedish Pomerania. von D?eln sent troops to relieve Hamburg, which was besieged by the French, without authorisation. For this he was court-martialled and was sentenced to be executed. He was however pardoned by the king.
See also: List of Swedish military commanders