Dillingen (page 3)

»Wasserballon«

A telegram of 25 February 1945 from Lfl. 6 to OKL had described Wasserballon’s purpose as ’the rapid destruction of bridges’ and urged its rapid development and delivery given that guided missiles had not proved entirely satisfactory in that role and drift mines only worked against pontoons. A week later Lfl. 6 was expecting to receive the ‘special droppable munitions … in the near future’, explaining that they would be carried on ETC 503 bomb racks. However, a note from Lfl. 6 dated 1 March suggests that Wasserballon was in fact a generic term for a family of munitions based on existing bombs with payloads modified to leave sufficient buoyancy for them to float with only the fuse breaking the surface. The adapted weapons were a BM 1000 mine with a 200 kg charge, the Flam C 500 with 300 kg and the Flam C 250 with 50 kg. The first of these was not expected to be ready for another three months and since it required water more than 3.8 m deep it was of no use against current targets. The Flam C 500 needed only 2 m but again availability was three months away. Currently only the Kugeltreibmine 41 was available but provided there were no hitches the Flam C 250 ought to arrive in mid-April.

NOTE: A Flam C 250 in its original configuration weighed 110 kg, 50 kg of which was attributable to the oil incendiary mixture and bursting charge.

On 28 March, II. Fliegerkorps indented for ETC 503 racks so that its Fw 190 Schlachtgruppen (i.e. Stab, II and III./SG 3) could carry the bombs under each wing and the centreline. Six days after that a preliminary report on the weapon was issued by the Bevollmächtigter für Brückenbekämpfung (Plenipotentiary for Bridge Attacks), describing it as: ‘… made from the casing of the former Flam C 250 [incendiary bomb with liquid filling] … specialised fuse installation triggered by the change in light FlamC250colour intensity when passing under a bridge …’ To date it had only been deployable from land but must now be delivered by air, with every effort being made to overcome the difficulties it had so far posed to pilots. With ballistics akin to those of the SC 250, the bomb must be dropped at a maximum speed of 400 km/h and a dive angle of 10º or less; at that speed the release height was 250 m. The specified angle of dive must not be exceeded or the bomb could ‘jump’ from the water by as much as 80 metres.

Experience to date suggested that a bomb dropped from 300 m up only needed a river 1.5 m deep to function as intended. It became live 90 seconds after entering the water, so must be dropped short of its target, the distance depending on the speed of the current. Sinking to 1.10 m, to it was carried along to its target with the light-sensitive fuse protruding above the surface. To prevent the enemy singling out the threat, it was suggested that tin cans or pieces of wood prepared to resemble the protruding fuse should be thrown into the river as decoys to draw his fire. It was thought that between eight and 10 of these weapons would be needed to destroy a bridge and the units foreseen as using them were I. and III./SG 1 (Fw 190 F), two Staffeln of NSGr. 8 (Ju 87 D) and II./LG 1 (Ju 88 A-4).

The first operational deployment of Wasserballon appears to have been against the Oder bridges at Kienitz and Zellin (Czelin, Poland) from 1700 GMT on 17 April. Some 16 Schlachtflugzeuge—presumably Fw 190s—from Lw.Kdo. Nordost took part, six with conventional bombs and 10 with Wasserballons. The targets could not be made out in the thick haze so there was ‘no observation of results’ and no conclusions were possible beyond saying that the bomb must be released from no more than of 200m and 400 km/h, limitations making it unsuitable for attacks on strongly-defended targets. A Ju 87 and two Fw 190s flew a ‘special operation’ against the same bridges that night but the only reported result was ‘reached target area’, a form of words used elsewhere for suicide missions on the Oder front.

NOTES:

(1) On the evening of 16 April Luftwaffenkommando Nordost commanded the following Schlachtflieger, all equipped with the Fw 190 and grouped under its I. Fliegerdivision (excluding Panzerblitz formations):


Stab SG 1	13	(8)
I./SG 1	36	(32)
II./SG 1	41	(32)
III./SG 1	36	(33)
Stab SG 3	6	(3)
II./SG 3	44	(33)

(2) Although Lorant and Goyat write—apparently based on veterans’ testimony—that Wasserballon’s ballistic momentum carried it through the water, everything above points to the bomb floating along, 1.10 m under the surface but with its fuse out of water (nose-up?). From my reading of the Plenipotentiary’s report, the two authors are in error when they say that Wasserballon exploded at a 5 m depth, where the darkness triggered the fuse. If it were underwater however there would have been no need of decoys, not to mention that a barometric trigger would seem a better choice. It may well be that they were relying on veterans’ memories of the briefing they received which in turn may have been tailored to maintain security regarding the weapon’s actual operation. The Plenipotentiary himself withheld some details from his subordinate formations on security grounds. Further, the targets known to have been attacked give the lie to any notion that the bomb detonated at a depth of 5 metres. This figure has only rarely been attained on the Oder at Kienitz while the Danube’s minimum depth at Dilliingen was given as 2.4 metres in the attack orders.

A 2019 post by ‘Thilo’ on the Forum der Wehrmacht website describes Wasserballon as floating nose-up, with its optical fuse above the water. He goes on to say that the fuse, once activated, set off a small charge which breached the bomb’s casing, causing it to sink. A timer exploded the weapon after a short delay, forcing a destructive column of water up at the bridge. In this reading Wasserballon exploited water’s incompressiblility like the British Upkeep ‘bouncing bomb’, however, the latter carried almost sixty times the charge and exploded at three or four times the depth.

Overnight on the 19/20th, 12 aircraft of Gefechtsverband Helbig undertook an ‘operation with Wasserballons (Oder)’ which targeted the bridges at Alt-Blessin (Stary Błeszyn) and Groß Neuendorf but again poor visibility over the following days precluded any visual or photographic reconnaissance to assess the damage. Unless they were dropped shortly before sunrise, the weapons concerned are unlikely to have been the Flam C 250 whose fuses needed daylight to work. More probable is the contact-fused Kugeltreibmine 41 (see above).

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