Role & capabilities
- Undersea autonomy experimentation
- Payload integration trials
- Crewed/uncrewed integration research
- Primary domain
- Underwater
- System type
- Autonomous underwater vehicle
- Developer / manufacturer
- MSubs
- Origin / production countries
- United Kingdom
- Other names
- Project Cetus; Cetus XLUUV
- Variants / configurations
- Named configuration; see the evidence and specification notes
- Operators / programme customers
- Royal Navy Fleet Experimentation Squadron — demonstrator
Evidence & current status
The Royal Navy explicitly describes Excalibur as a non-operational demonstrator. Delivery is not treated as combat or patrol service.
XV Excalibur is the large underwater demonstrator produced by Plymouth-based MSubs under the Royal Navy's Project Cetus. It gives the Navy a physical test platform for exploring how large autonomous underwater vehicles can be supported, controlled and integrated with crewed forces. Its role includes evaluating bespoke payloads and the broader practical demands of operating vehicles of this scale.
The Royal Navy unveiled the 12-metre, 19-tonne vehicle in May 2025 after delivery earlier that year and harbour and sea acceptance work. It assigned Excalibur to the Fleet Experimentation Squadron and described a two-year programme of further trials. Crucially, the same announcement explicitly stated that the demonstrator would not perform operational duties. Its existence and acceptance testing should therefore not be interpreted as an operational autonomous-submarine fleet entering service. The public dimensions identify the demonstrator configuration. Detailed endurance, depth and sensor performance remain unfilled here where the reviewed sources do not provide a reliable baseline.
Sourced specifications
Figures apply to the named configuration. Maximum values are not guaranteed operating performance.
| Specification | Reported value | Context & source |
|---|---|---|
| Configuration | Extra-large autonomous underwater demonstrator | Published specification for the cited configuration; payload, environment and speed affect performance. Source ↗ |
| Hull / propulsion | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Dimensions | 12 m long; 2 m across | Published specification for the cited configuration; payload, environment and speed affect performance. Source ↗ |
| Displacement / mass | 19 tonnes displacement | Published specification for the cited configuration; payload, environment and speed affect performance. Source ↗ |
| Payload | Bespoke experimental payload accommodation | Published specification for the cited configuration; payload, environment and speed affect performance. Source ↗ |
| Endurance | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Range | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Speed | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Operating depth | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Sensors | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Communications / control | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
| Launch / deployment | Not established in the reviewed public sources. | Public data gap; no estimate or neighbouring variant value substituted. Source ↗ |
Documented milestones
XV Excalibur unveiled
The Navy named the delivered demonstrator and described a two-year trials programme.
Read the announcement ↗Cetus contract announced
The Royal Navy announced its MSubs contract for an extra-large underwater experimental vehicle.
Read the announcement ↗
Publication history
- — Added sourced land and maritime coverage with domain-specific evidence and limitations.
Suggest a correction to this entry →
Follow the evidence
Source types identify who makes the claim. Programme milestones and supplier statements should be read in context.