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MRS3 is a working colocation data center in Marseille, France, built inside the former Martha submarine-base structure: an unfinished German WWII military project that never entered service as a submarine base. Interxion opened its first data-center phase there on July 1, 2020; the facility is now listed as operating by Digital Realty.
What was the Martha bunker?
Martha was a German submarine-base project built in Marseille’s port in 1943. The structure was never completed and was never put into service as a submarine base, according to project architect Kardham. Reuters reported that the intended base was designed to accommodate up to 20 U-boats; that figure describes the plan, not submarines that actually operated from the site. Kardham’s project account and Reuters’ 2019 report describe the history and proposed use.
The structure’s scale and concrete construction helped make it a candidate for reuse. In its 2020 announcement, Interxion described terraced reinforced concrete up to 5.5 metres thick, a 250-metre length and a 12-metre surrounding wall. The company also said the structure could withstand 10-tonne bombs. Those are company-reported historical specifications, not independent structural-test results. Interxion’s launch announcement sets out those claims.
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How did it become a data center?
Interxion adapted the former military structure into MRS3, preserving its overall form while accommodating modern data-center infrastructure. Kardham describes the design challenge as working within planning constraints while retaining the building’s distinctive shape. Kardham’s project record outlines the architectural approach.
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Interxion announced the first phase opening on July 1, 2020. Its announcement described a three-phase development, with about 7,100 m² of planned IT space and 16.5 MW of capacity; the first phase comprised about 2,300 m². These were figures in the company’s 2020 launch announcement, rather than a statement of today’s delivered capacity. Read Interxion’s 2020 announcement.
What are MRS3’s current listed specifications?
Digital Realty’s current facility page lists MRS3 as an operating site and gives the following facility details. These are operator-published specifications, not third-party audit findings. Digital Realty’s MRS3 page is the source for the current listing.
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| Specification | Current listing |
|---|---|
| Total building size | 11,850 m² |
| UPS and cooling redundancy | N+1 |
| Energy | 100% renewable energy |
| On-site security | 24/7 |
| Video surveillance | CCTV with 30-day backup |
| Access controls | Biometric or photo-badge access |
Building area and IT-room area are different measures: the 11,850 m² listing is for the total building, while the 7,100 m² figure in project materials refers to IT space or rooms. Capacity figures also vary by source and date: Interxion announced 16.5 MW in 2020, while Kardham’s project record lists 17 MW and 7,100 m² of IT rooms. Kardham does not show a publication date for that record, so the 17 MW figure should be understood as its project-record specification, not assigned an invented date. Kardham’s project record.
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How does MRS3 fit into Marseille’s data-center network?
MRS3 is part of Digital Realty’s Marseille campus alongside MRS2 and MRS4. Digital Realty says those facilities benefit from river cooling and reports 18 submarine cables connected to the campus. The cable total is campus-wide; it does not mean all 18 cables terminate in MRS3. Digital Realty’s Marseille campus page describes the campus features and connectivity.
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The conversion also had a substantial announced budget: Reuters reported in 2019 that Interxion planned to invest €140 million in transforming the site. This was the investment plan reported at that time, not necessarily the final works budget. Reuters’ 2019 report.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Why reuse a WWII structure for computing?
The unusual pairing is practical as well as architectural: a massive existing shell was adapted to host contemporary computing infrastructure, while the design sought to preserve its overall form. Today, MRS3 serves the commercial colocation market, and Digital Realty lists it as part of a Marseille campus connected to international submarine-cable routes. The facility’s present role is a data center; Martha’s intended role as a submarine base was never realized.
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