Drone Swarms That Harassed Navy Ships Off California Demystified In New Documents

A major release of documents provides the highest level of detail yet about mysterious drone swarms involving U.S. Navy ships off California.

byAdam Kehoe and Marc Cecotti|
Navy UAP Drones California
Documents on drone encounters of Southern California. Credit:NAVY via FOIA. Navy via FOIA

The War Zone has received a highly significant new set of documents from the U.S. Navy via the Freedom of Information Act about a series of enigmatic drone swarm events that occurred in the waters off Southern California in 2019. These incidents have come to be woven into an ongoing discussion about unidentified aerial phenomena, traditionally known as UFOs. In previous weeks, top defense officials told Congress that the 2019 swarm incidents were caused by drones. These new documents leave little doubt in that regard.

The documents include unprecedentedly detailed briefing materials and photographs from more than a half dozen incidents. Among these new incidents are previously unknown events that occurred in the early months of 2019 and were assessed by the Navy to involve intelligence collection operations.

Speculation has swirled around these incidents in the last year, following high-profile leaks of night vision video footage depicting objects with an apparent triangular shape overflying Navy vessels. The unusual appearance of the objects led to widespread speculation that they were otherworldly UFOs, despite evidence that the Navy regarded the objects as conventional drones. The video was recently discussed in a congressional hearing on Unidentified Aerial Phenomena as an example of a solved case. According to Deputy Director of Naval Intelligence Scott Bray, the video was definitively identified as an unmanned aerial system (UAS) following a second swarm event that occurred off the East Coast of the United States this year.

Our previous coverage began with a series of drone incidents that occurred on July 15th, 2019 approximately seventy nautical miles off the east coast of San Clemente Island. A tranche of deck logs from Navy vessels indicated that several ships had encountered drones over an extended period of time.


We previously reported the close presence of several civilian vessels in conjunction with these sightings, notably the Hong Kong-flagged bulk carrier MV Bass Strait. Our initial investigation leveraged automatic identification system (AIS) ship location data in conjunction with deck logs to reconstruct the incidents. The terseness of the deck logs and limitations in AIS data left several unanswered questions, such as the origin of the drones and the specifics of their flight behavior. Many of those questions can now be answered.

Among the new documents released to us is this briefing slide, which depicts the course of the Bass Strait relative to the Arleigh Burke class destroyer USS Paul Hamilton, also abbreviated here as PHM, as it transited to a scheduled port call in Long Beach, California. The briefing slide states that the Navy assessed that the commercial cargo ship was likely conducting surveillance on Navy vessels using drones, or unidentified aerial vehicles (UAV). A timeline of events shows that the surveillance lasted for just under four hours. In that time, multiple UAVs were spotted operating around the destroyer.  


An email sent on July 15th matches these details and references a number of images and one video file. These images were captured by the Ship Nautical Or Otherwise Photographic Interpretation and Exploitation team, or "SNOOPIE team." These teams consist of sailors trained to conduct onboard photographic intelligence in order to document unknown contacts and events of interest.


The images from the incident include these photographs of what appears to be the Bass Strait. The Bass Strait's owner and operator, Hong Kong-based Pacific Basin, did not reply to several requests for comment.


Similar briefings were prepared by other Navy vessels involved in the incidents. The Ticonderoga class cruiser USS Bunker Hill (BKH) noted as many as 11 drones operating nearby. A note on the slide states that the cruiser unsuccessfully attempted to contact the Bass Strait. It also indicates that the UAS incident continued after the Bass Strait departed the area. The exact duration of the incident is less clear, though the timeline indicates drones were spotted over a period of about four and a half hours.

The timeline also indicates that Bunker Hill's AN/SPY-1 radar system held "valid tracks" of the drones, including up to an altitude of 21,000 feet. Although an image of one of the drones is hard to identify in the slide, a caption describes the objects as “Quadcopter style UAS.” 


Finally, the USS Ralph Johnson (RJN), another Arleigh Burke class destroyer, also prepared briefing slides about the incident. They described intermittent radar tracks of the objects. A legend on the slide shows at least four UAS tracks, and the timeline mentions that lights from as many as 10 additional drones were visually spotted. 


Notably, Ralph Johnson assessed the UAS as operating in a “safe and professional approach” that was "in accordance with the internationally recognized COLREGs 'rules of the road' and internationally recognized maritime customs" in a draft public affairs statement. It is unclear if this assessment was shared by the other vessels.


An email dated July 14, 2019, sent while the incident was in progress, stated that there was a pause between periods of UAS activity. The email further states that no counter unmanned aerial system (CUAS) measures were deployed during the first phase and that the USS Ralph Johnson was not at that time equipped with “DRAKE or other C-UAS equipment.” DRAKE refers to Northrop Grumman’s Drone Restricted Access Using Known EW (DRAKE) system, a portable anti-drone platform. Records previously released to us demonstrated that DRAKE systems were deployed to several ships later in July 2019. This email confirms that at least some ships were entirely without CUAS equipment, which was less common in the 2019 timeframe.

A US Navy sailor training with a Northrop Grumman DRAKE electronic warfare system. USN

Events From July 17th To July 30th, 2019

Our previous analysis of deck logs indicated that other events occurred several weeks after the initial events of July 14th and 15th. These events were significantly less clear than the earlier incidents. This is in part because traditional deck logs were not available from Littoral Combat Ships (LCS) due to their use of digital records. Briefing slides can now fill some of these gaps.

The first of these incidents came just days after the initial events. Documents show that the Arleigh Burke class destroyer USS Russell, also referred to by its hull number, DDG 59, and the abbreviation RSL), first reported an interaction with three unknown UAS on July 17th, 2019 approximately 62 nautical miles southwest of San Nicolas Island. The Russell has attracted particular attention in the last year as the vessel that captured the leaked “flying triangle” footage. A briefing slide states that the objects were not distinguishable by the naked eye. The incident occurred over a period of approximately one hour. Notably, a night scope image of an apparently triangular object can be seen in the lower left corner. According to the timeline, one of the objects hovered over the ship at an altitude of about 700 feet.


Included among the documents were other images, now highly recognizable from video leaks and congressional hearings. In congressional testimony, defense officials explained that "the triangular appearance is a result of light passing through the night vision goggles, and then being recorded by an SLR camera."


The July 21st And 25th Incidents

On July 21st, the USS Paul Hamilton again reported seeing a group of drones. In this incident, the drones were assessed to likely be operated by a “local fisherman operating personal quadcopters.” A note indicates that no videos were captured of the drones due to distance.


Several days later, the USS Gabrielle Giffords (GBG), an Independence class Littoral Combat Ship, encountered a set of four drones in the same general vicinity. The drones orbited around the ship during a flight of its own MQ-8B rotary-wing reconnaissance UAS, prompting the nearby USS Pinckney (PKN) to assist in an investigation. The USS Gabrielle Giffords also queried what it believed to be the UAS "homeplate" a term used to indicate an aircraft's home airfield or ship.

Three small boats were identified nearby, with one identifying themselves as a small fishing vessel. The USS Gabrielle Gifford's MQ-8B was deployed again after refueling, but was unable to locate the four UAVs.


The July 30th Incident

Deck logs previously indicated that another more complex incident occurred around July 30th, again involving multiple Navy vessels. It should be noted that in this time period, records show that some ships appear to have deployed and trained with a variety of counter drone technologies and techniques. These included the previously mentioned DRAKE system, a man-portable backpack that allows sailors to jam the radio frequency signals used to control drones. The USS Russell in particular is known to have these systems onboard prior to the incident on July 30th.

The exact nature of what happened in this incident was previously unknown due to heavy redactions in ship logs. However, the newly released documents contain several clarifying details.

A briefing slide from the USS Russell shows that the ship observed two groups of lights over a period of about three hours. During that time, several drones flew directly over the USS Russell. As in the earlier incidents, an unidentified pleasure craft was operating in the vicinity. The USS Kidd, another Arleigh Burke class destroyer, was also nearby, but did not report a visual sighting of the drones. The timeline indicates ships were directed by "GZ" but it is unclear what this abbreviation refers to.  


A lengthier description states that a total of five unknown drones approached the USS Russell in the course of the incident. It also states that communication was never established with the nearby pleasure craft, though a standard UAS warning script was read over the radio.


A contemporaneous email from the USS Russell confirms these details, and further indicates that the DRAKE team was activated.


Deck logs further revealed that radiofrequency data was captured from the drones during the incident. These details were obtained after The War Zone successfully appealed extensive redactions of the ship logs. A reference to both the drones and the “RF” data can be seen below:


In addition to the USS Russell, the USS Paul Hamilton also reported observing multiple drones on July 30th. Though there are relatively few details, a briefing slide describes that multiple drones were observed, with some coming as close as 200 yards (closest point of approach; CPA) to the ship’s bow.


As in the other cases, a contemporaneous email report and draft public affairs statement provide further details. The USS Paul Hamilton reported observing and identifying the drones visually via “technical means.” Although an unknown vessel is referenced, it is unclear if this is the same ship that was operating near the USS Russell.


Notably, the public affairs statement characterizes the behavior of the drones as dangerous, and not in accordance with the “rules of the road” or “internationally recognized maritime customs.”


Finally, a photograph of one of the drones was included with the report:


Entirely New Incidents In Early 2019

While our initial investigation focused on the cluster of drone events in July described above, these new records also indicate that at least two other significant drone swarm events occurred in the waters off Southern California earlier in 2019.

The first incident occurred on March 30, 2019. The USS Harpers Ferry (HFY), an amphibious dock landing ship, reported seeing as many as 8 unknown drones flying directly over the ship at an altitude of about 500 feet.


A draft public affairs statement further added that the drones were thought to be “conducting collection operations” on the ship.


A month later, the USS Zumwalt, the Navy's most advanced surface combatant, encountered a set of six drones on April 24, 2019. In this incident, drones crossed the flight deck of the ship while flying in a “consistent pattern” that did not alter “course, speed, or altitude.”


Unclear images of the drones are also attached to the report, though few details can be made out:


Drone Swarms: A Growing Issue Since 2019

Based on these documents, the U.S. Navy had at least eight distinct encounters with groups of multiple drones in the waters off California in 2019. The circumstances of these incidents vary widely. Some incidents were assessed to be “collection operations” while others were attributed to local fishermen operating personal quadcopters. While drone overflights of Navy vessels are not new, the use of multiple drones simultenously is an emerging phenomenon.

Drone swarms are an increasingly common occurrence, though precise statistics about the total number and severity of incidents are hard to come by. The War Zone has previously created an interactive database of drone incidents reported to the Federal Aviation Administration (FAA), accessible here. While this data offers some perspective on the scope of incidents, it suffers from a number of limitations inherent in ad hoc reports. The Biden administration issued a new directive to address data collection, among other provisions, regarding drone incidents earlier this year.

To get a sense of how frequently drone swarms are occurring in recent years, we recently spoke with DroneSec, a drone cybersecurity firm based in Melbourne. DroneSec collects and categorizes drone incident reports on a global basis. The company also co-facilitates the Global Drone Security Network conference, a recurring series that brings together a wide spectrum of industry, academic, and government specialists.

DroneSec CEO Mike Monnik told us that incidents involving multiple drones have increased significantly worldwide since 2019. CTO Jared Page added that “definitely in the last two years there has been a marked increase in activity related to swarms.” The company’s threat intelligence database has registered approximately 151 swarm incidents in that time. According to Page, public reports started to escalate in late 2019.

Though some of these incidents involved things like attempts to hack civilian light displays, many fall in the realm of more nefarious activities. Monnik and Page emphasized that it is increasingly easy for criminals to field drone swarms. DroneSec cited a 2020 Department of Justice audit focused on the use of drones in delivering prison contraband as an example of how swarm technology is increasingly used in practice. The report referenced one notable incident that involved the simultaneous use of 15 drones to distract and overwhelm a prison facility’s security systems. Monnik noted that in recent years it has become more common for criminals to use one or more drones as a “canary” to assess the defenses of a target. Once a target has been shown to be defenseless or easily overwhelmed, subsequent drones can be deployed to accomplish a particular mission.

The team at DroneSec also spoke to the complexity of comprehensively defending against drone threats, emphasizing that no single technical solution exists yet. In the case of the naval incidents, some ships indicated that they did not yet have any operational C-UAS technologies. Monnik and Page explained that drone detection itself remains a very complex problem that often requires specialized radar and radio frequency equipment that is not guaranteed to work in all circumstances.

Addressing these particular security gaps has been a clear priority for the Navy in recent years, with a number of high-profile projects involving directed energy weapons. These concerns are shared broadly throughout the military and United States government. Last year Marine General Kenneth McKenzie Jr. said that drones are "the most concerning tactical development since the rise of the improvised explosive device in Iraq." Battlefield commanders in Syria and Afghanistan have both had to constantly contend with drone threats. Oil facilities in Saudi Arabia have been significant targets of drone attacks in recent years, with massive economic consequences. Within the western hemisphere, drones have been used by non-state criminal actors in Mexico both as means of smuggling and as weapons of war. Domestically, drone swarms have been an issue for nuclear reactor facilities and critical industrial infrastructure.

In addition to the technical challenges posed by drones, the Department of Defense has also struggled to encourage aviators and service members to report what they see, even if they can’t clearly identify it. The unusual commingling of the longstanding UFO issue with drones has arguably created a potent cultural blindspot that can be exploited by adversaries. Arguably, the year-long confusion surrounding the leaked footage from the USS Russell attests to this problem.

Meanwhile, America's adversaries, especially China, are investing massively into drone swarm capabilities, especially for use in the maritime environment, for wartime use and for dual-role applications. Swarming capabilities are seen even by top U.S. think tanks and the Pentagon as being so critical to future conflicts that they could be decisive in a major peer-state battle, such as one over Taiwan.

Many Questions Remain

In the previous year, it has been difficult to get definitive answers regarding these incidents. In our initial investigation, public affairs officials from the Navy, Coast Guard, and Federal Bureau of Investigations all either declined to comment or referred our questions to the Department of Defense’s spokesperson handling the unidentified aerial phenomenon (UAP) issue. Public affairs officials in multiple agencies have been consistently tight-lipped on this matter, with most information coming strictly through the Freedom of Information Act.

Following last month’s congressional hearing about UAP, we sought further clarification about the national security implications of drone swarms. While the Department of Defense spokesperson acknowledged our questions, they have not provided a comment at the time of writing. The details available in these official Navy documents stand at odds with the widespread perception of Chief of Naval Operations Michael Gilday's statement last year that the Navy was unaware of who was operating the unidentified aircraft. We now know that in several instances, the Navy had significant information about the potential origin of the drones deployed in some of the most serious incidents, although the specific operators remained unknown.

Although many questions remain about these incidents, one thing is clear. Active surveillance of key naval assets is being conducted in areas where they train and employ their most sensitive systems, often within close proximity to American shores. Deputy Director of Naval Intelligence Scott Bray took pains to emphasize in a recent congressional hearing that the military "train as they would fight." Espionage collected in these areas is of extreme value to potential adversaries and poses a serious and ongoing national security threat. The War Zone previously laid out this reality and its implications in great detail in this feature.

We will continue to seek clarification regarding these incidents and keep readers updated as we analyze this complex new set of documents.

Updated June 16, 2022. Subsequent release of video from the Navy makes it more likely that the small dark dots in the images of the Bass Strait are part of the structure of the ship than drones.