Doubling Noise, Unannounced Arrivals, New Troop Deployments: Visualizing the ‘Quiet Burden Increase’ at Iwakuni Base Through Numbers

In a city with a military base, the burden does not come all at once. It accumulates slowly and quietly.

For those living around Iwakuni Base, the fiscal year 2024 has been a year of “moving numbers.” According to noise measurement data released by Yamaguchi Prefecture and Iwakuni City, the frequency of noise occurrences around the base has reached approximately double the level compared to before the relocation of carrier-based aircraft (prior to fiscal year 2017). It has been several years since the operations of the FA-18 Super Hornets, which were relocated from Atsugi Base, began in earnest—amidst what should have been a familiar daily life, only the numbers have silently increased.

Overlaying this situation are the unannounced arrivals of Australian military aircraft and the temporary deployment of the F-35B unit. Each of these could be dismissed as a “temporary event” when viewed in isolation. However, when these three are considered together, what emerges is the very structure by which the costs of coexistence with the base are being rewritten without the knowledge of the residents.

In this article, we will track the three phenomena of noise, arrivals, and troop deployments through numbers and timelines, while considering “who benefits from this and who bears the burden.”

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1. Noise—What “Doubling” Means

When discussing the noise issue at Iwakuni Base, the starting point is the completion of the relocation of carrier-based aircraft in March 2018. Approximately 60 aircraft moved from Atsugi Base (Kanagawa Prefecture), making Iwakuni one of the largest U.S. military air bases in the Far East. At that time, the government explained that “it will continue to monitor the noise situation after the relocation and take necessary measures.”

Six years after the relocation, data from multiple measurement stations set up around the base by Yamaguchi Prefecture shows that the frequency of noise occurrences has approximately doubled from pre-relocation levels. Notably, the occurrences exceeding 70 decibels—levels that disrupt everyday conversation—have significantly increased.

What should be noted here is the substance behind the number “doubling.” The impact of noise cannot be measured simply by frequency. Factors such as how much early morning and nighttime flights are included, the duration of each occurrence, and the peak sound pressure levels all influence residents’ perceptions. Complaints about noise received by Iwakuni City have also been on the rise in recent years, indicating that the numbers and the lived experiences are aligned.

Noise is not just a problem while it is heard. Interruptions to sleep, disruptions in conversation, and lapses in concentration—when these become integrated into daily life, people eventually begin to say they have “gotten used to it.” However, getting used to something is not the same as being unaffected by it. For children in their growth period and elderly individuals with pre-existing health conditions, chronic exposure to noise accumulates as a health risk. The World Health Organization (WHO) recommends that aircraft noise levels at night should be below 45 decibels (Lnight). How the measurement values around Iwakuni Base compare to this standard is a matter that requires verification by the authorities using international benchmarks.

The “necessary measures” promised by the government before the relocation have been implemented in the form of subsidies for residential soundproofing and requests to the U.S. side for consideration of flight routes. However, soundproofing construction is predicated on keeping windows closed, which is incompatible with a lifestyle that requires opening windows in the summer. While systems exist, there is a gap between these systems and the realities of daily life. To label the situation as “addressed” while leaving the discrepancies between rules and reality unacknowledged is not a sincere approach to the facts.

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2. Unannounced Arrivals—The Erosion of the Premise of “Prior Notification”

In 2024, military aircraft from the Australian Air Force arrived at Iwakuni Base without prior notification. Iwakuni City Mayor Yoshihiko Fukuda expressed his discomfort regarding this matter, stating, “It is regrettable that there was no prior information provided.”

The core of this issue lies not only in noise and safety. The framework that has supported coexistence between the base and the community—the operational rule between Japan and the U.S. that “prior information will be provided regarding the arrival of foreign aircraft”—has been shaken by the variable of allied military aircraft.

In recent years, Iwakuni Base has strengthened its role as a hub for multilateral training that goes beyond the Japan-U.S. alliance. The frequency of military aircraft arrivals from allied and friendly nations, including Australia, the United Kingdom, and France, has been on the rise. The traditional notification framework based on the Japan-U.S. Security Treaty and Status of Forces Agreement was designed with a bilateral context in mind. As multilateral operations become the norm, the rules regarding “who notifies whom about what” have not kept pace with these changes.

The mayor’s statement that “consideration for the local community is lacking” is not merely an emotional argument. Prior notification is the minimum procedure for residents to accept the presence of the base and is the very foundation of trust in coexistence. When this procedure is omitted, residents lose not only information but also the sense that “their lives are being considered”—in other words, the very precondition for coexistence.

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3. Temporary Deployment of F-35B—The Timeframe Implicit in “Temporary”

In 2024, against the backdrop of escalating tensions in the Middle East, the U.S. Marine Corps’ F-35B Lightning II unit temporarily deployed to Iwakuni Base. While there is already a permanent F-35B unit (Marine Fighter Attack Squadron 121, VMFA-121, with 16 aircraft) stationed in Iwakuni, an additional unit has been deployed.

Mayor Fukuda expressed concern, stating, “Even if it is temporary, the impact on the region is significant.” This concern is grounded in fact. The F-35B is a short takeoff/vertical landing (STOVL) aircraft, and particularly during vertical landings, the exhaust heat and noise exceed that of conventional aircraft. The U.S. Department of Defense’s environmental impact assessment also indicates that the operational noise of the F-35B is greater than that of the FA-18 under certain conditions. If the training of the temporarily deployed unit is added to the operations of the permanent unit, both the frequency and intensity of noise occurrences will increase.

What is noteworthy here is the ambiguity of the term “temporary.” Military “temporary deployments” often do not have a clear deadline. If tensions in the Middle East persist, the deployment may extend, and eventually, what is considered “temporary” may be reinterpreted as “permanent”—such precedents have been repeated at bases across Japan, including Okinawa.

Iwakuni Base has seen a significant increase in the number of aircraft since the relocation of carrier-based aircraft in 2018, and with the permanent deployment of the F-35B, it has become a hub for the operation of cutting-edge aircraft. The structure of temporary deployments overlapping with this is a gradual expansion of base functions—what can be termed a “quiet burden increase.” Each individual instance can be explained as being “within the prescribed range,” but it remains unclear who will verify the accumulated total.

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4. When Three Phenomena Overlap—The Increase in Burden as a Structure

Doubling noise, unannounced arrivals, temporary deployment of F-35B. When viewed individually, each of these phenomena has its own “reason.” The relocation of carrier-based aircraft is based on Japan-U.S. agreements, unannounced arrivals are a byproduct of multilateral cooperation, and the deployment of the F-35B is a response to international circumstances—all of which can be rationally explained in the context of security.

However, the perspective from those who bear the burden is different. The three phenomena are overlapping at the same time, in the same city, above the same residents. And it is difficult to say that the system for visualizing, verifying, and explaining the total burden to the residents is functioning adequately.

The Japanese government has established systems such as soundproofing subsidies, relocation compensation, and reorganization grants as measures for areas surrounding bases. Iwakuni City has received approximately 4.9 billion yen annually (at peak) as reorganization grants, which have been used for the city’s finances and infrastructure development. While these grants do indeed benefit the region, if their existence becomes a license to say “compensation has been provided” and dulls the verification of the burden itself, then the system cannot be considered healthy.

What is important is not that “there is compensation, so there is no problem,” but rather that “the actual burden is accurately understood and the appropriateness of compensation is continuously verified.” Are the placements of noise measurement stations sufficient? Is the measurement data made easily accessible to residents? Is the feedback from complaint handling functioning?—the details of the system reveal the seriousness of the commitment to coexistence.

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5. Who Benefits and Who Bears the Burden?

The strengthening of Iwakuni Base’s functions is positioned as supporting the deterrence of U.S. forces in the Indo-Pacific region and enhancing the reliability of the Japan-U.S. alliance. The benefits of this are broadly and thinly distributed in the form of national security for Japan as a whole.

On the other hand, the costs are localized. It is the residents of Iwakuni who hear the noise, feel anxiety over unannounced arrivals, and bear the exhaust heat of the F-35B overhead—these burdens are concentrated on those living in specific areas. The benefits of security are enjoyed by the entire nation, while the burdens are disproportionately borne by the residents surrounding the base—this asymmetry has been repeatedly pointed out as the essential structure of base issues.

That is why the visualization of the burden is necessary. Tracking the “quiet burden increase” through numbers, arranging them chronologically, and presenting them as a structure. This is not to oppose or support the base. It is a foundational effort to accurately understand the costs of coexistence and to consider as a society who will bear those costs and how.

The city of Iwakuni has a long history of walking alongside the base. The trust that has been built up over that time has been supported by each individual procedure—prior notifications, noise measurements, responses to complaints. When the system quietly creaks, it is always those who live within that system who first notice.

Numbers do not have a voice. However, when lined up, their outlines become visible. The doubled noise, the omitted notifications, the ambiguous “temporary”—beyond those outlines lies the lives of people spending summer in rooms with closed windows.