Leaving the academy, Pegna was posted to the Naval Arsenal of La Spezia, where he had the opportunity to experience his first flight as an observer in a two-seat reconnaissance [seaplane].
Pegna became in charge of the establishment of the seaplanes department, initially at Pesaro, and then moving to Porto Corsini, Brindisi and Taranto.
In 1915 Pegna was transferred to Milan, assigned to the supervision of the work by aeronautics companies, which were accelerated into technological design and production due to the outbreak of World War I.
The military authorities believed that the company's decision had been influenced directly by Pegna, and as a result he was put trial and sentenced to three months of arrest for disobedience.
In 1917 Pegna continued his aeronautics research by designing an aircraft suitable for stratospheric flight, while he was assigned to the Air Force Technical direction.