Dual rebreathers in practice: example experiences from the Wetmules and COBRA Divers

Closed-circuit rebreathers have opened new frontiers in technical diving, but rebreathers are not invulnerable and therefore a 'bailout' gas supply is required. For extreme dives, open-circuit bailout is logistically impossible. This has led teams to adopt dual rebreather configurations, where a second rebreather serves as bailout. This article presents operational experiences from the Wetmules and COBRA Divers, who independently developed dual rebreather practices for extended range diving. The teams evolved contrasting approaches through extensive field testing. The Wetmules initially adopted partially integrated configurations, sharing components between rebreathers to reduce complexity for deep dives with straightforward access to dive sites. COBRA Divers used fully independent dual rebreathers, prioritising complete redundancy for remote locations with challenging logistics. Both developed techniques to ensure the operational status of the inactive rebreather including gas content variability, buoyancy control, and fault detection. Real-world experience validated theoretical benefits while revealing additional considerations. Both teams significantly reduced open-circuit bailout requirements, enabling extended penetrations and depths that were previously extremely difficult. Key operational insights included maintaining breathable gas mixtures in inactive loops, regular integrity checks, and managing variable buoyancy. The approach introduced new challenges: increased task loading, maintenance requirements, and novel failure modes specific to inactive rebreathers, showing that equipment redundancy does not automatically enhance safety. Dual rebreathers extend operational envelopes but introduce significant complexity. Benefits include eliminating gas switches during emergencies and maintaining optimal decompression profiles. However, inactive rebreathers remain vulnerable to undetected failures and demand higher operator proficiency. The contrasting approaches - integration versus full independence - reflect different operational priorities and mission parameters. This article contributes operational experience to support informed decision-making within the technical diving community.