ISC Defence Intelligence

Technical Summary

Approximately 1.6 million tonnes of World War II–era munitions remain on the floor of the Baltic Sea along Germany’s northern coastline, concentrated primarily in the waters near Kiel Bay and Lübeck Bay. The ordnance inventory comprises aerial bombs (primarily SC 250 and SC 500 general-purpose high-explosive types), artillery projectiles ranging from 75 mm to 380 mm calibre, naval mines (both moored contact and ground influence types), depth charges, torpedo warheads, and rocket munitions. The majority were deliberately dumped by Allied occupation forces between 1945 and 1948 under Operation Grunerberg and subsequent disposal programmes, with additional items originating from wartime combat losses, naval engagements, and emergency jettisoning.

The primary explosive fills across this ordnance inventory are 2,4,6-trinitrotoluene (TNT), amatol (TNT/ammonium nitrate mixtures in ratios of 80/20 to 40/60), and cast pentolite (PETN/TNT 50/50). German aerial bombs of the SC series typically contained cast TNT or amatol fills with total Net Explosive Quantity (NEQ) ranging from 62.5 kg (SC 250) to 250 kg (SC 500) per item. Fuzing mechanisms on dumped munitions include both impact and time-delay types; many fuzes have degraded to an unpredictable state, rendering the items extremely hazardous to handle. The Explosive Ordnance Disposal (EOD) classification for these items is Category A (confirmed explosive ordnance) with an assessed sensitivity status of “unpredictable” due to advanced corrosion and potential fuze degradation.

A twelve-person multinational scientific team from the GEOMAR Helmholtz Centre for Ocean Research Kiel is conducting three-week research expeditions aboard the RV Alkor to map hazard concentrations using autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs). Sediment sampling and water column analysis have confirmed the presence of TNT and its primary environmental degradation products — 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT) — in both seawater and marine organisms. Traces of these carcinogenic compounds have been detected in shellfish tissue sampled from dumping site proximity.

Analysis of Effects

Corrosion and Energetic Release Pathways

The Baltic Sea presents a uniquely adverse environment for ferrous ordnance casings. Its low salinity (7–8 parts per thousand, compared to 35 ppt for open ocean) combined with seasonal temperature cycling between 2°C and 18°C accelerates differential corrosion of carbon steel casings. Research indicates that typical World War II munition casings (carbon steel, wall thickness 8–15 mm) in Baltic conditions experience perforation within 70–100 years of immersion. With the majority of items dumped between 1945 and 1948, the current period (2025–2045) represents the critical window during which casing integrity failure and energetic release will peak.

Once casing perforation occurs, seawater ingress dissolves the exposed TNT fill at a measured rate of approximately 0.1–1.0 mg/cm²/day, depending on temperature and water flow. For a single SC 250 bomb containing 62.5 kg of cast TNT, complete dissolution would require decades. However, the environmental hazard arises not from individual item dissolution but from the aggregate TNT mass across 1.6 million tonnes of ordnance entering the marine environment simultaneously across thousands of dumping sites.

Hazard Classification

The submerged ordnance retains its original Hazard Division classification. Aerial bombs with TNT fills are classified HD 1.1 (mass detonation hazard). Naval mines with combined explosive and initiating mechanisms present HD 1.1 or HD 1.2 hazards depending on fuze state. The advanced corrosion state introduces an additional hazard: crystalline TNT deposits on external casing surfaces are friction-sensitive and may detonate from mechanical impact during recovery operations. This renders conventional EOD render-safe procedures more hazardous than for intact items.

Personnel and Safety Considerations

EOD personnel engaged in Baltic maritime ordnance recovery face compound hazards that exceed standard land-based UXO clearance operations. The combination of advanced corrosion, unpredictable fuze states, crystalline energetic surface deposits, and underwater working conditions demands specialised protocols.

The Lübeck Bay pilot disposal programme, funded at €100 million, employs a floating platform from which commercial divers and ROVs locate, assess, and recover individual items. Recovery follows International Mine Action Standards (IMAS) 09.30 (EOD) procedures adapted for the maritime environment. Items are categorised on the seabed using visual assessment and non-destructive testing prior to any lift operation. High-risk items — those with intact fuzing, visible crystalline energetic deposits, or advanced casing compromise — are destroyed in situ using shaped donor charges where seabed conditions and environmental constraints permit.

The wreck of the Franken, a German Navy tanker torpedoed by Soviet forces on 8 April 1945 in Polish waters, presents a combined hazard of approximately 200 tonnes of fuel oil co-located with an assessed ammunition cargo. This wreck requires specialist multi-hazard assessment combining maritime salvage, environmental containment, and EOD expertise. Cordon distances for underwater detonation of HD 1.1 items in shallow water (<30 metres depth) should account for surface shock wave propagation, which extends the effective hazard radius to approximately 500 metres for items with NEQ exceeding 50 kg, per STANAG 2929 maritime EOD safety distances.

Data Gaps