Three prototypes were ordered in April 1941 with serials 41-19501, 41-19502 and 42-7164. The I-1430 was having continued development problems and could not be delivered in time, so it was replaced by an Allison V-1710-47, similar to that powering the P-39. Each prototypes tested different wing and tail configurations: 41-19501 had a rounded vertical tail, but squared-off tailplane tips; 41-19502, a squared-off fin and rudder and large wing fillets; and 42-7164 had all its flight surfaces squared off. The XP-39E proved faster than standard Airacobra, reaching a maximum speed of at during tests. However, the XP-39E was considered inferior to the stock P-39 Airacobra in all other respects, so it was not ordered into production.