The series 500/501/510 were the first low wing fighters designed by Emil Dewoitine after years of parasol fighter aircraft. They were a sort of transitional fighter with its fixed landing gear and open cockpit which entered service around the middle of the 1930s. Soon obsolete, by the time the WW2 started the Dewoitines were relegated to training duties.
In this photo a D.501 of the 8e Escuadre de Coopération (G.C.I/8 ex-3 C 3) Aéronautique Navale (Naval Aviation). The D.501 were equipped with one of those famous Hispano Suiza “Moteur Canon”: a 12Xcrs engine that incorporated a 20 mm Hispano-Suiza S7 cannon between its cylinder banks.
To say that they’re beautiful is a serious understatement.