Practically all single-engine day fighters of WW II shared the same layout:

(1) Engine in front driving a (2) tractor propeller, (3) forward-firing armament, (4) single fin, (5) low-wing in a monoplane configuration, and (6) crew of one.

Only a few fighters offered different alternatives and none proved very successful:

a) biplane fighters (like the I-153 and Fiat CR.42) which were proven obsolete very early.
b) The P-39 Airacobra (and later P-63 Kingcobra) offered an engine behind the pilot. It found acceptance by the Soviet VVS, but the layout was not duplicated by any air force, and all single-engine day fighters of the late-war period stuck to the conventional layout, and
c) The Boulton Paul Defiant (picture)
Instead of forward-firing weaponry, it was equipped with a four-gun turret operated by an additional crew member.

In theory, the Defiant could attack bombers from the beam, where their defensive gun positions were less effective. In practice, this configuration proved unsuccessful. The additional crew member and the turret added weight and the power-to-weight ratio of the fighter was an anemic 0.347 hp/kg while that of the Bf 109E-3 (its main opponent) was 0.421.

As a result, the 109 was notably superior in climb, max. speed, and acceleration. It also had much superior firepower, and it could outturn the Defiant. It was also easier to maneuver a fighter into position for firing when the guns were facing forward.

Actual combat experience confirmed the performance statistics.
On 13 May 1940, six Defiants from 264 Squadron (along with 6 Spitfires from 66 Squadron) faced German fighters for the first time. In the ensuing battle with JG 26, 264 Sqdrn lost five Defiants and shot down one 109.

During Dunkirk (31 May) the Defiant Sqdr once again battled JG 26 and lost 3 aircraft. JG 26 also shot down 5 Hurricanes and lost only 2 fighters.

The Defiant was relegated to night fighting, but even in this capacity, it was removed quickly from front-line service (no radar-equipped squadron was formed with Defiants. Production ceased early 1942).