Two nations are at war over something rather trivial, but offenses have been perpetrated here and there such that the conflict has escalated from a couple of guys shooting each other to massive bombing runs by both sides which can kill thousands.
The bombing runs are a la the strategic bombing campaigns of Britain and Germany during World War II:
Wings of bombers set out in groups of four, flying four abreast. They're not quite heavy bombers, but more like the Heinkel He 111:
There are a few squadrons of heavy bombers, though, like the Avro Lancaster:
The bombers are protected by fast, single-seat fighters armed with four front-facing machine guns and two rear-facing machine guns. They're similar in speed and size to the Supermarine Spitfire:
There are about ten fighters per four bombers - enough heavy defenses to hold off most attacks.
Technologically, all of the aircraft have systems similar in technology those of the 1960s. The one significant difference is that the engines are not jet engines. On this world, electric engines have been developed, making anything running on oil obsolete. The jet engine was never developed.
However, one side has developed technology that can emit electromagnetic pulses. Concentrated pulses can travel about fifty feet before dissipating. Each of the enemy fighters has been modified so that it only carries two (forward-facing) machine guns but has turrets above and below the cockpit that can fire an electromagnetic pulse. The one below the cockpit is weaker so that it can be fit in without causing inconvenience to the landing gear.
With proper aim, one of these fighters can render part of a bomber useless. Targets depend on the bomber type; on two-engine bombers the main target is one of the engines, in an attempt to knock out the power and control. One four-engine bombers, the strategy is to take out the rear gunner with the machine guns, then fly overhead and deliver two pulses in the general area of the cockpit, hopefully destroying instruments and potentially killing crew members.1
The other side (non-EMP guys) are not too pleased about this, and they'd like to figure out a mechanism that can protect all the critical components (e.g. engines, fuselage, bomb bay, etc.) of the bombers from EMP attacks. They've hit on the idea of a Faraday cage, which can be really effective . . . but it's been found that holes from bullets can inadvertently cause considerable damage to the cage, which drastically reduces its ability to stop the EMP pulses (hence the strategy used when attacking heavy bombers). They've also read this pdf, but they're not at all convinced that any of the shielding ideas could remain uncompromised after machine gun attacks. Bullet-proof walls have proven to be ineffective, because of certain (as-yet unknown) characteristics of the enemy's bullets.
What can the bomber crews do to protect themselves and their airplanes?
1 Bombers now are designed with escape routes and landing gear doors that do not involve electricity and can be operated manually. Same goes for fighters.