Piotr R. Nowak

Explosive weapons may cause damage through both blast loading and fragmentation of their casings. Although air-detonated ordnance has been extensively studied, fragmentation hazards from underwater munitions remain underexplored, and therefore no standardised procedure exists to calculate safe standoff distances as a function of depth and charge mass in naval environments. This significantly hampers the safety planning process for underwater explosives ordnance disposal activities. Building on prior laboratory investigations of underwater fragmentation, this study extends the analysis toward full-scale applicability by estimating maximum fragmentation ranges and applying injury-criteria models to assess associated hazard limits. A series of well-controlled small-scale experiments compared cased explosive charges detonated in air and at varying submersion depths. Three casing configurations were tested to quantify the influence of depth and casing configuration type on fragment generation, in-flight behaviour, and size–velocity distributions. High-speed videography and in-situ witness panels were utilised to track fragmentation post-detonation and estimate velocities during flight and after impact. An in-house analysis code with optical and panel data was developed to compute fragment trajectories, maximum ranges, and soft-tissue penetration probabilities using established injury thresholds. Results indicate a pronounced reduction in fragment count, velocity and launch angle with increasing submersion depth, producing substantially shorter predicted penetration distances for all tested submerged charges. This paper outlines a practical methodology for scaling experimental observations toward larger charge masses and discusses implications for risk assessment and mitigation during underwater munitions clearance operations.

The threat related to explosive materials in the water domain has not yet gotten the attention it deserves. For many years in European Countries, this hazard was reduced to unexploded explosive ordnance (UXO) or abandoned explosive ordnance (AXO). During peacetime, Europe was focused on economic growth and governments, with public support, were cutting military spending below NATO’s target of 2% of GDP (Grand, 2023). The Navy was the first victim of the mandatory budget cuts. Investments in new equipment and the development of modern procedures were put on hold. The Russian attack on Ukraine and the Nord Stream sabotage was a wake-up call for most NATO members. An attack on EU vital maritime infrastructure with the help of sophisticated improvised devices, outdated widely used weapons and explosives, or unidentified ordnance is more likely than ever. At the same time, the size of the maritime area to be protected and the nature of the threats make it difficult to track the adversary and link the explosive event to a certain country or organization. If such devices are found within important maritime infrastructure or sensitive systems, non-violent methods may be used by Navy specialists to defeat the explosive weapons. NATO commitments to strengthen maritime capabilities are visible in the increased defense spending and the demand for new equipment and capabilities.

The use of wood as a structural element is still commonly used in constructions, not only in civil engineering but also in military applications. The access to this material, its processing and the ability to create individual joins without advanced equipment are reasons why wood remains an important material in military operations. Another important argument is the use of wooden structures to build local crossings for the benefit of the state economy. The speed of construction and the cost of making for example a driving deck are many times lower. This is quite an important factor influencing the decision of local governments to rebuild temporary crossings. Moreover, the skilful use of this material can significantly help the army in terms of durability and effective manoeuvrability. Engineering troops can build shelters for people and equipment, as well as low-water and underwater bridges and crossings for armoured fighting vehicles from wood. Any destruction of wooden structures planned by the engineering troops must be based on calculations derived from knowledge and experience. This article presents experiments on contact explosions of wooden structural elements. Pine beams with an equal diameter of 23 cm were tested in the military field. The wooden log destruction has been inventoried and the damage to particular wooden tissues was quantified by using different amounts of explosives. Also, professional military analyses were conducted to determine the explosive mass to destroy such wooden logs. Later, the computed values were compared with the results obtained in the field experiment and a damage parameter of energy criteria for pine wood was determined for the constitutive model of wood including damage.

The clearance of underwater ordnance is one of the most complex tasks entrusted to appropriately trained and equipped soldiers. State-of-the-art knowledge in this area is rarely published and is most often possessed by a narrow group of navy specialists. The aim of this paper was to find a link between the existing mathematical models for the peak pressure of underwater explosion with measurements of small charge detonations for long ranges to the observation point in real life scenarios. We have shown the results of the research in which the underwater explosion tests were presented for different TNT equivalents and standoff distances and thus distance ratios. The curves of pressure versus time of ignition were reported. The measurements were confronted with empirical formulas. The comparison showed large, but expected, differences, since the empirical formulas are advised for smaller distance ratios. Based on the conclusions from the study, the new methodology to identify the loading from underwater explosions based on a database collected was postulated. By creating a survey methodology for ships crew for recording explosion parameters, a large number of events can be registered without a strict setup of the test area. The database obtained can be used by military commanders to identify the explosive hazard in the Baltic Sea region.