The Japan Maritime Self-Defense Force (JMSDF) implemented a major organizational reform at the end of March 2026. As part of this restructuring, it established the Patrol and Defense Group (哨戒防備群) and assigned some of its most modern surface combatants, including the Mogami-class frigates, to this formation.
This newly established Patrol and Defense Group carries significant implications for the JMSDF. Traditionally, one of the service’s primary peacetime missions has been the surveillance and monitoring of foreign naval vessels operating in waters surrounding Japan. In recent years, however, the rapid expansion of the People’s Liberation Army Navy (PLAN) has led to a marked increase in the frequency and scale of Chinese naval activities near Japan. In response, the JMSDF has been compelled to deploy not only destroyers but also missile boats, replenishment ships, and even minesweepers to meet the growing demand for maritime domain awareness operations.
Such operational patterns have placed considerable strain on the JMSDF’s surface fleet. In particular, the heavy burden of peacetime surveillance missions has limited opportunities for training, thereby posing challenges to maintaining overall readiness and proficiency.
To address this issue, the JMSDF established the Patrol and Defense Group as a specialized formation dedicated to missions such as monitoring the activities of foreign naval vessels in Japan’s surrounding waters. By consolidating peacetime surveillance and patrol duties within this group, the JMSDF can enable its broader fleet—including destroyers—to focus more intensively on their primary wartime roles and contingency preparedness.
The headquarters of the Patrol and Defense Group is located in Yokosuka, with five subordinate Patrol and Defense Units newly formed under its command. These units are distributed across five JMSDF bases throughout Japan.
Patrol and Defense Group vessels: FFM, PG and OPV
At present, each Patrol and Defense Unit is equipped with Mogami-class frigates (FFMs) and Hayabusa-class guided-missile patrol boats (PGs). The Mogami-class vessels were previously assigned to Escort Divisions 11 through 15—the so-called “two-digit escort divisions”—which were primarily responsible for coastal defense. Following the March reorganization, these divisions were disbanded and reorganized into the Patrol and Defense Group. Mogami-class frigates will be focusing on patrol duties following the organizational reform.
The Mogami-class represents the JMSDF’s latest generation of stealth-oriented frigates. Their armament is relatively limited, consisting of a Mk 45 5-inch gun, anti-ship missiles, and SeaRAM. Although a modification program is underway to equip these ships with a 16-cell Mk 41 Vertical Launch System (VLS)—with ships from the seventh hull onward fitted from construction—this system is intended to deploy the Type 07 Vertical Launch ASROC (VLA), and does not include ship-to-air missile capability.
Starting in 2027, the Patrol and Defense Group will be reinforced by a new class of vessels—the Sakura-class offshore patrol vessels (OPV). The Sakura-class has a standard displacement of approximately 1,900 tons, an overall length of 95 meters, and a beam of 12.0 meters. Its armament is limited to a single 30mm autocannon. These vessels are purpose-built for surveillance and monitoring missions—roles that the Japan Maritime Self-Defense Force has not traditionally emphasized in dedicated platforms—and their equipment and capabilities are deliberately kept to the minimum required for such tasks.
Despite their relatively light configuration, the Sakura-class maintains a maximum speed of around 25 knots, which is comparable to that of conventional destroyers. In addition, due to their limited mission set and compact hull design, the crew size is reduced to approximately 30 personnel. This high level of automation is reportedly supported in part by advanced bridge systems derived from reduced-manning technologies increasingly adopted in the commercial shipping sector. Construction costs are also relatively low, with the first four vessels budgeted at approximately ¥35.7 billion (about $238 million) in total—equating to roughly ¥9 billion (about $60 million) per ship.
In terms of aviation capability, the aft multi-purpose deck allows for takeoff and landing operations by all types of helicopters currently operated by the JMSDF. However, the vessels lack the capacity to embark and sustain these aircraft. Instead, there are plans to equip the ships at a later stage with the V-BAT vertical takeoff and landing (VTOL) unmanned aerial system developed by Shield AI. This addition is expected to significantly enhance wide-area maritime surveillance capabilities, including the ability to detect and track vessels operating at extended ranges.
That said, the role of the Sakura-class is not limited to visual monitoring of foreign naval vessels. According to the JMSDF, these ships are slated to receive electromagnetic intelligence (ELINT) collection systems at a later stage. While the exact nature of this equipment has not been disclosed, it is likely intended to intercept and analyze electromagnetic emissions such as communications signals and radar transmissions from foreign military assets.
In fact, in recent years, the JMSDF has already been observed equipping vessels deployed for extended durations in open-ocean environments with such ELINT capabilities. For example, the lead ship of the Uraga-class minesweeper tenders, JS Uraga, has been confirmed to carry ESM systems—specifically the SME-150 and CRS-Naval—manufactured by the Swedish defense company Saab. These systems are designed to collect and process electromagnetic emissions, suggesting a precedent for similar capabilities being installed aboard the Sakura-class OPVs.
In this way, the Patrol and Defense Group is expected to evolve beyond a force solely tasked with monitoring foreign naval movements. By conducting continuous electromagnetic intelligence collection in peacetime and exerting a persistent presence, it may also serve as a means of applying strategic pressure on potential adversaries. This represents a new form of deterrence for Japan in the maritime domain.