B-26 Marauder 320th Bomb Group

 

Marauder Bridge Busting
by Victor C. Tannehill

 

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There were many factors to be considered and many alternatives to be decided upon in planning and carrying out a B-26 mission against a rail or road bridge.

First came the question of which bridge to hit to most effectively cut the Germans off from their Supplies. The answer came from analysis of intelligence information and aerial intelligence.

Once a particular bridge was singled out for attack because of the bottleneck blasting it would create, operational policy was to keep on hitting it with as many consecutive missions as necessary to knock it out before going on to the next one. That way the Germans didn't have time to concentrate their flak.

Of course one bridge being cut did not deter the enemy for long. The Germans simply took their trains to the edge of a bombed viaduct, unloaded their supplies into trucks and hauled them around to the other side to be loaded on another train going south. So, in order to maintain a complete break in a rail line many cuts within a short distance had to be made to prevent this train-truck shuttle.

The enemy countered by dispersing bridge repair battalions and spare steel spans along the rail lines so that within a few hours after the bombardment replacement could be underway. Our answer was to step up the frequency of B-26 attacks.

The best approach to the target had to be decided on, and this was difficult at times. Some bridges were so small or so well hidden in mountain folds that picking them up at all became a real problem. The approach also had to take known flak positions into account.

Axis of attack was another consideration. Most bridges were attacked at a ninety degree angle, from altitudes of 9,000 to 12,000 feet. This allowed the bombardier to make deflection errors half the length of the bridge and it gave him an excellent horizontal line to put the cross hair of his bomb sight on. In most cases the drop pattern was set to have bombs first strike just short of the bridge and then extend across it. Larger bridges were usually hit at about forty-five degrees, depending on the range or string spread of the bombs.

The weather report had to be carefully and accurately analyzed.

Wind had to be considered. An upwind approach, for instance, improves accuracy by decreasing the formation's ground speed so that a standard length bomb run can start at a point closer to the target.

Formation was another factor. Marauder bridge-busting was best done by flights rather than by "boxes

A critical decision had to be made on the intervalometer (bomb fall) setting. To hit a thirty-foot wide bridge, bombs of the lead ship of each flight which carried the Norden bombsight might be set to fall at, say, sixty-foot intervals. Wing ship bomb intervals might be set at thirty feet. The lead ship's string would be set to start short of the target to compensate for the dropping lag between lead and wing ships. The sixty-foot interval would bring the last few bombs of the lead ship across the bridge. Wing ship strings would then be directly across the bridge, their thirty-foot setting preventing any "jumps".

Size and types of bomb to be used and fuse settings also had to be deter-mined.  Bombs on bridge busting missions were generally one or two thousand pound demolition types fitted with either delay or instantaneous fuses, sometimes with an armor-piercing case.

It was important to use the smallest bomb possible so more bombs per airplane could be carried. A 1,000-pounder would cut a bridge not more than twenty-five feet wide - if the bomb was properly fused. If a bridge was more than twenty-five feet wide, a 2,000-pound bomb had to be used, but this cut the probability of one airplane obtaining a hit at least in half.

Delay fuses (usually .01 seconds) permitted the bombs to penetrate deep into the bridge before exploding. Instantaneous fuses, of course, blew up the bombs on contact and were generally used on steel suspension bridges to prevent the bomb from crashing through the structural girders and exploding in the open air beneath.

On a particularly tough and rugged bridge, such as one with a heavy reinforced concrete floor or one of granite, bombs with an armor-piercing shell were used. This gave the bomb a chance to penetrate without rupturing and then explode. The delay was usually .025 seconds, enough to permit penetration into the concrete so that the explosion would push outward, crumbing the bridge.

Sometimes selected B-26s scattered through the formation would drop a few long-delay bombs in an effort to hinder later bridge repairs. These bombs would burrow into the earth a number of feet and then curve out laterally. They couldn't be excavated before they might go off and the enemy couldn't tell exactly where they were unless he did plenty of digging. They might explode as long as twenty-four hours after dropping and this posed both a psychological and a real hazard to repair workers.

  • Victor C. Tannehill
    Copyright 1978

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