Philadelphia Experiment: What the Records Can—and Cannot—Confirm
If Navy records certify only degaussing-level ‘invisibility’, what can the surviving archive no longer certify about the 1943 Philadelphia claim?
This case survives in a narrow set of institutional summaries and one collection-level finding aid, not in citable primary pages within this package.
- ONR sheet: alleged secret naval experiment in Philadelphia in 1943
- Allende-attributed claim: a ship rendered invisible during the experiment
- NHHC definition: degaussing can make a ship ‘invisible’ to magnetic mine sensors, not to human eyes
- Archives West: Carlos Allende papers, 1943-1994 (bulk 1957-1984)
- NHHC: stated review of USS Eldridge deck log and war diary
These points mark the stable edge of what this evidence set can certify, and they also mark where certification stops.
NHHC’s statement that it reviewed USS Eldridge’s deck log and war diary (Aug–Dec 1943)
On the NHHC Online Reading Room page for the Philadelphia Experiment, one sentence appears as an administrative conclusion about what was checked.
The sentence uses the phrase ‘The Archives has reviewed’ and names two record types: a deck log and a war diary. It does not present the records themselves on that line.
The same sentence pins the start of the review window to Eldridge’s commissioning on 27 August 1943 at the New York Navy Yard.
It also states the review continued through December 1943. The sentence does not, by itself, quote locations, entries, or movements from the underlying pages.
In this form, the page preserves a claim about an archival action rather than the artifacts that action examined.
The only citable element here is the statement that the deck log and war diary were reviewed within that time window, without the underlying pages attached.[1]
This can certify that a review is claimed and time-boxed, but it cannot certify what the deck log or war diary pages contain; the next unresolved step is access to the actual pages.
The ONR information sheet’s core frame: an alleged 1943 Philadelphia experiment
The NHHC-hosted ONR information sheet opens by defining the story as ‘An alleged secret naval experiment conducted by the Navy in Philadelphia in 1943.’
That wording keeps the claim bounded by place and year, while holding it in the register of allegation rather than documented operation.
The sheet does not, in the cited lines, supply operational records or a chain of documentation that would let this package certify the event beyond that framed allegation.[2]
What the record attributes to Carlos Allende, and what it does not
In the same ONR information sheet, the invisibility element is explicitly placed under attribution: ‘During the experiment, according to Allende, a ship was rendered invisible.’
Within this evidence set, that line is the boundary between an institutional summary voice and a named-source claim.
The validated material here does not include Allende’s underlying documents, so this package cannot certify the supporting detail that might sit behind the attribution.[2]
The only Navy-language definition of ‘invisible’ available here: degaussing
The NHHC page provides a single bounded meaning for ‘invisible’ in Navy-adjacent explanatory language: ‘It could be said that degaussing, correctly done, makes a ship ‘invisible’ to the sensors of magnetic mines, but the ship remains visible to the human eye …’
The only Navy-language definition of ‘invisible’ available here: degaussing
That sentence supports one specific mechanism claim only, tied to magnetic mine sensors rather than optical disappearance.
This validated set does not include WWII-era degaussing manuals, directives, or technical reports, so the mechanism cannot be expanded here beyond that single institutional sentence.[1]
The finding aid that proves the papers exist, without proving what they say
Archives West preserves a collection-level record titled ‘Carlos Allende papers, 1943-1994 (bulk 1957-1984)’.
In this evidence set, that title line can certify existence and date span for an Allende-associated collection.
It cannot, by itself, certify specific correspondence content, specific claims, or a stable timeline of how the story was told inside the papers, because the contents are not provided here.[3]
A secondary explainer exists, but it cannot carry certification here
A Military.com explainer is validated as present in this package, and it can function as a secondary narrative baseline.
It does not change the main constraint in this file: the certified anchors remain the NHHC and ONR summary sentences and the Archives West finding aid line.
When primary artifacts are not included, a secondary explainer cannot supply missing dates, locations, or technical steps inside a strict documentary boundary.[4]
Where certification stops in the Philadelphia Experiment file
The opening question turns on two different uses of the same word: ‘invisible’ as an alleged event claim, and ‘invisible’ as degaussing language tied to magnetic mine sensors.
This evidence set can certify that the ONR sheet labels the story as alleged and attributes the rendered-invisible claim to Allende.
It can also certify that NHHC presents a bounded degaussing sentence, and that NHHC states an Archives review of Eldridge’s deck log and war diary from commissioning on 27 August 1943 at the New York Navy Yard through December 1943.
Certification stops because the primary deck log and war diary pages are not included here for quotation, wartime degaussing manuals are not included here for mechanism detail, and the Allende papers are represented only by a finding aid line rather than accessible contents.[1]
FAQs (Decoded)
What do the institutional documents call the Philadelphia Experiment?
The ONR information sheet describes it as an alleged secret naval experiment conducted by the Navy in Philadelphia in 1943. Source: NHHC, ONR information sheet.
In this evidence set, what can ‘invisible’ mean in Navy-language terms?
Only the degaussing sentence is available here, and it limits ‘invisible’ to magnetic mine sensors while stating the ship remains visible to the human eye. Source: NHHC, Online Reading Room page.
Did NHHC claim it checked USS Eldridge operational records for 1943?
Yes, the NHHC page states that ‘The Archives has reviewed the deck log and war diary’ from commissioning on 27 August 1943 at the New York Navy Yard through December 1943. Source: NHHC, Online Reading Room page.
Does the ONR sheet present the invisibility claim as an institutional fact?
No, the sheet places it under explicit attribution by saying it occurred ‘according to Allende’. Source: NHHC, ONR information sheet.
What can be certified about the Carlos Allende papers from the validated material here?
Only that a collection titled ‘Carlos Allende papers, 1943-1994 (bulk 1957-1984)’ is described in a finding aid, without certified access to its contents in this package. Source: Archives West, finding aid record.
Why does this article not quote deck log entries or technical manuals?
Because the validated sources here reference a review and provide summary sentences, but they do not include the primary deck log pages, war diary pages, or wartime degaussing manuals for direct quotation. Source: NHHC, Online Reading Room page.
This case file is preserved within the forbidden science archive, where institutional summaries and fringe case files mark the boundaries of what documentation can and cannot certify.
Sources Consulted
- NHHC, Online Reading Room Philadelphia Experiment page. history.navy.mil, accessed 2025-02-17
- NHHC, ONR information sheet on the Philadelphia Experiment. history.navy.mil, accessed 2025-02-10
- Archives West, finding aid record for the Carlos Allende papers. archiveswest.orbiscascade.org, accessed 2025-02-03
- Military.com, explainer article on the Philadelphia Experiment. military.com, accessed 2025-01-27
A Living Archive
This project is never complete. History is a fluid signal, often distorted by those who record it. We are constantly updating these files as new information is declassified or discovered.
