The Photoflash Bombs that Illuminated Cities

Photoflash bombs are a type of explosive ordnance with the purpose of illuminating vast areas of the ground for night-time aerial reconnaissance. Resembling a typical bomb, they produce a brief, intense burst of light hundreds of millions of candlepower bright.

In fact, they were so bright that they could easily cause serious vision loss if looked at with the naked eye.

For the brief moment the photoflash bomb lasted, the ground below became lit as if it was day time, making high resolution, accurate reconnaissance photos possible at night.


Aerial Reconnaissance

Almost as soon as the aircraft itself was developed, military planners were able to see the enormous potential in military applications. While today we typically associate military aircraft in offensive roles (bombers, fighters, strike aircraft etc.), the first military aircraft were used for reconnaissance.

This gave militaries a view of the battlefield previously unseen for all of human history.

By the time of the Second World War, aircraft were no longer mere curiosities or novelties; they had evolved into indispensable tools of warfare, playing a crucial role in surveillance and the gathering of intelligence.

Aerial reconnaissance aircraft and its pilot during WWI.
Aerial reconnaissance camera mounted on a B.E.2c in 1916.

However, there remained some significant limitations, particularly regarding operations conducted at night or during adverse weather conditions.

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Unlike today, where extremely sensitive cameras, radar and thermal imaging have effectively eliminated the obstacle of darkness, back then the night would put a stop on aerial reconnaissance.

The necessity to operate at night, coupled with the constraints of early photographic technology, created a pressing challenge: how could one effectively capture images in low-light conditions from a fast-moving aircraft?

F.8 Mk II aerial camera.
Type F.8 Mk II aerial camera to be mounted in a Spitfire photo reconnaissance aircraft.

Traditional means of illumination, like flares, were fleeting, fairly dim for photography and often inconsistent, making them unsuitable for detailed aerial photography.

Additionally, flying at lower altitudes to achieve better photographs was fraught with risks, making it an unfavorable option.

To address these challenges, military researchers and engineers began to explore the possibility of creating a device that could produce a powerful, momentary burst of light, bright enough to illuminate vast swaths of territory below.

Photo flash bombs being loaded into a Mosquito.
Photoflash bombs being loaded into the bomb-bay of a Mosquito in 1944.

This effort culminated in the development of the photoflash bomb. Unlike conventional explosives, the primary purpose of these bombs was not to destroy, but to illuminate.

The Photoflash Bomb

These bombs were dropped from reconnaissance aircraft fitted with cameras, and would detonate at a predetermined altitude. The instantaneous flash illuminated the landscape below, allowing for a short window of opportunity to capture clear aerial photographs.

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Photoflash bombs resembled a conventional bomb from the outside, but were thin-walled and contained explosive fillings that burned bright.

Photoflash bomb over Italy.
A photoflash bomb detonating over La Spezia in Italy, lighting up the ground below. A Lancaster silhouette can be seen near the bottom of the image.

The detonation height of photoflash bombs was critical, as if this happened too high, the light would dissipate before reaching the ground; too low, and it might not cover the desired area.

In addition, the exceptionally bright light emitted from photoflash bombs was enough to cause vision-damage if seen with the naked eye, so care had to be taken by crews to avoid this.

The Design Of Photoflash Bombs

The foundational component of photoflash bombs was typically magnesium, a metal renowned for burning extremely bright when ignited.

Magnesium burns with an intense white light, which made it the perfect candidate for producing the brightness needed. However, simply igniting magnesium wouldn’t suffice; the challenge lay in controlling its burn rate and ensuring an even distribution of light.

To achieve this, magnesium was often mixed with other chemicals or agents to control the intensity and duration of the burn.

M46 photoflash bomb diagram.
A US M46 photoflash bomb. This bomb was 48 inches long, 8 inches wide and had a candlepower of 500,000,000.

This mixture was then encased in a specially designed, thin-walled shell that would ensure proper dispersal of the ignited material, allowing for a consistent and broad illumination. The power of photoflash bombs varied, but one type, the US M46, had a peak intensity of 500 million candlepower.

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A crucial component of the photoflash bomb’s design was its triggering mechanism. As mentioned, the bomb had to detonate at a precise altitude to maximize its effectiveness.

Engineers, therefore, integrated altimeter-triggered fuses. These fuses ensured that the bomb would ignite at the optimal altitude, providing the best possible conditions for aerial photography.

Illumination bomb over Libya.
Photoflash bomb dropped by the RAF lighting up Tobruk in Libya, 1942.

The fuse would be started by a wire attached to the aircraft, which was pulled when the bomb was dropped.

Given the fleeting nature of the flash (around 200 milliseconds), synchronization with the reconnaissance aircraft’s cameras was imperative. The aircraft used for these operations were typically equipped with specialized cameras designed to work in tandem with the photoflash bombs.

These cameras boasted fast shutter speeds and sensitive film, allowing them to capture sharp images in the brief illumination window provided by the bomb’s flash.

Operational Impact

Prior to the advent of photoflash bombs, the cloak of darkness provided a protective layer for military activities. Movements, fortifications, and other strategic operations could be concealed from prying eyes, with the hope that any actions under the cover of night remained obscured until daylight.

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Photoflash bombs disrupted this advantage. With their ability to illuminate large expanses of terrain, night time became a viable window for reconnaissance, allowing military commanders to stay updated on enemy movements and activities round the clock.

Photoflash over Turin in Italy.
Turin in Italy is completely lit by a photoflash bomb in this image.

Daylight reconnaissance missions posed significant risks. Aircraft, clearly visible against the daytime sky, became easy targets for anti-air defenses and enemy fighters.

The ability to conduct surveillance operations under the cover of darkness dramatically reduced the risk of detection. Even if the flash from the bomb alerted the enemy, the quick nature of the operation and the darkness of the surroundings provided a considerable level of protection to the reconnaissance aircraft.

However photoflash bombs were more sensitive to mishandling than conventional explosives due to the nature of the filling. A US ordnance manual states “Extreme care should be exercised in handling these bombs, because the charge is very sensitive to friction, shock, and temperature.”

Photoflash over Plouha.
Photoflash illuminating the French town of Plouha.

The detailed images captured during these nighttime operations offered insights not just into enemy troop movements, but also into their supply lines, infrastructure, and other critical assets.

This wealth of information provided a strategic edge, allowing for more informed decision-making and more precise targeting in subsequent operations.

Beyond the tangible operational advantages, the mere knowledge that the enemy had the capability to “see” in the dark had a psychological impact.

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It created an environment of heightened alertness and, in some cases, could induce a sense of paranoia and fear among enemy ranks, unsure of when they might be observed.