By Paul R Salmon FCILT, FSCM
In a world of increasingly contested supply chains and constrained budgets, defence organisations face a dual challenge: building resilience against disruption while driving efficiency. One often-overlooked lever that addresses both is interchangeability of spare parts.
Interchangeability enables parts, systems, or sub-systems to be swapped or substituted with alternatives—whether sourced from different suppliers, partner nations, or commercial stock—without the need for redesign or adaptation. This principle not only strengthens supply chain resilience but also offers significant opportunities to reduce logistics footprints and overall costs.
Why Interchangeability Matters in Defence Logistics
Defence equipment is often designed for bespoke performance. While this optimises capability, it can lead to a proliferation of unique spare parts across fleets, creating a sprawling and fragile support network. Interchangeability counters this by embedding adaptability into systems from the outset.
1️⃣ Enhancing Resilience
In disrupted environments—be it a global pandemic, geopolitical instability, or contested supply chains—interchangeable parts allow alternative suppliers or local stock to be used, maintaining operational readiness when primary sources are unavailable.
Example: Allied forces in NATO can leverage interchangeable components and shared maintenance stocks to keep equipment operational in joint theatres.
2️⃣ Reducing Logistics Footprint
Standardising and interchanging parts across multiple platforms shrinks the number of unique items that must be stored, transported, and managed. For deployed forces, this means fewer containers, fewer convoys, and lower exposure to risk in contested supply routes.
Example: A single type of alternator or filter usable across multiple vehicle types means less inventory needs to be held forward in operational theatres.
3️⃣ Driving Cost Efficiencies
Fewer unique spares enable economies of scale in procurement. Suppliers can produce larger batches of standardised components at lower cost, while defence organisations reduce warehousing needs and obsolescence risks.
Example: A logistics chain supporting 50 unique types of tyres is inherently more costly than one supporting 5 interchangeable variants.
The Hidden Costs of Non-Interchangeability
Lack of interchangeability can severely undermine both resilience and efficiency:
🚨 Single Points of Failure
A unique spare reliant on one supplier creates vulnerabilities if that supplier fails.
📦 Inventory Bloat
Proliferation of bespoke parts requires larger stockpiles and more storage space, increasing the logistics footprint.
💷 High Lifecycle Costs
Managing, tracking, and moving many low-volume spares drives up support costs over the equipment’s life.
In deployed environments, these factors compound, leading to larger, more vulnerable supply chains and higher sustainment costs.
Designing for Interchangeability
Achieving interchangeability is not an afterthought; it requires deliberate choices in design and procurement:
🔧 Modular Design
Designing systems with modular, replaceable components enables easier substitution in-service.
📜 Standards and Specifications
Adopting common specifications for critical components across platforms (e.g., batteries, filters, fasteners) allows cross-fleet support.
🤝 Allied Collaboration
Harmonising standards with partner nations enables shared stocks and mutual support in joint operations.
Strategic Benefits Beyond Resilience
Incorporating interchangeability delivers broader strategic advantages:
✅ Agility in Supply Chains
Alternative suppliers or parts can be activated without delays or costly redesigns.
✅ Lean Logistics
Smaller, lighter supply chains reduce transport requirements and exposure in contested environments.
✅ Sustainability Goals
Fewer unique spares mean reduced waste and lower carbon emissions across the supply chain.
✅ Better Industry Engagement
A focus on standardised, high-volume parts strengthens supplier resilience and attracts a wider industrial base.
Defence Example: Tyre Interchangeability
A UK vehicle fleet operating in multiple theatres had historically used several bespoke tyre variants. This necessitated larger forward stockpiles and resulted in frequent shortages when particular tyres were delayed in transit. A move to a small number of interchangeable tyre sizes not only reduced the number of spares required by 40% but also enabled troops to source replacements from local suppliers, enhancing resilience and reducing costs by millions of pounds annually.
Conclusion: A Small Change, a Big Impact
Interchangeability of spare parts might seem like a technical detail, but in practice it is a strategic enabler of operational agility and efficiency. By reducing the logistics burden, enabling rapid substitution, and lowering lifecycle costs, it empowers defence supply chains to deliver capability where and when it matters most.
As the UK MOD pursues its Integrated Operating Concept and seeks leaner, more adaptable support networks, interchangeability should be a central design and procurement principle. It is not just a cost-saving measure; it is a cornerstone of resilient, agile, and sustainable defence logistics in an era of uncertainty.
