Current military operations involve complex omnipresent threats, resulting in the need for all soldiers, regardless of occupational speciality, to wear body armour during operational deployment. Body armour is typically comprised of both hard and soft armour and is designed to provide ballistic, fragmentation and stab protection. The weight load and bulk of body armour, which is influenced by the materials used and extent of hard and soft armour coverage of the body, has the potential to affect a soldiers physical mobility on the battlefield. Intuitively it would appear logical that as the external load a soldier carries increases there is an associated decrease in their ability to move on the battlefield. Indeed studies have shown that external load can affect performance of key military tasks and thus compromise mobility when compared to an unloaded state. For example, Holewijn (1992) demonstrated that for every 1kg increase in external load, there was an average performance loss of 1% during tasks including jumping, sprinting, hand grenade throwing and obstacle course completion. The levels of protection proposed as part of the Tiered Body Armour System (Tiered BAS) have not been systematically evaluated and it is therefore unknown whether the weight increments of each level have a significant impact on soldier mobility. This study has quantified performance effects of the Tiered BAS and therefore examined the trade-off between passive protection (body armour coverage and ballistic rating) and active protection (soldier mobility). The results of this study can be reliably employed in conjunction with other important factors (e.g. thermal load) to inform Tiered BAS procurement decisions for the Australian Army. Secondly, results may be used to develop a commander's guide to BAS selection (used in conjunction with threat profile information) on operations. The aim of this study was to assess the impact of different levels of body armour protection (Tiered BAS) on soldiers' mobility. Specifically; Quantify baseline soldier mobility in a military clean skin (MCS) condition. Assess, measure and compare mobility under an Individual Combat Load Carriage Equipment (ICLCE) chest webbing system (control condition) and four levels of Tiered BAS. Underpin findings by correlative investigation with basic physiological and or anthropometric characteristics. Provide summary recommendations of the effects of weight load on soldiers' mobility.