Analysis: Taiwan’s Tien Kung IV Air Defense Surpasses U.S. Patriot PAC-3 in Range.

Taiwan’s new Tien Kung IV air defense system outpaces the U.S. Patriot PAC-3 in range, marking a major step in boosting its defenses amid rising tensions with China.

As reported by Taiwan Defense News Tracker on September 15, 2025, Taiwan’s National Chung-Shan Institute of Science and Technology (NCSIST) introduced the Tien Kung IV surface-to-air missile system, also known as TK-4 or Sky Bow IV, at the Taipei Aerospace and Defense Technology Exhibition in September 2025. This was the first time the missile, its launcher, and associated radar were shown publicly. The system is part of the Strong Bow program that began in 2015 and represents the latest step in the Tien Kung family, following TK-1, TK-2, and TK-3.
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The Tien Kung IV is reported to intercept missiles at altitudes of up to 70 kilometers, surpassing the US-made Patriot PAC-3 system, which is capable of engaging targets at altitudes of around 24 kilometers. (Picture source: X/OSINTWarfare & Taepodong)

According to Taiwan’s Ministry of National Defense, the TK-4 program has passed combat evaluation and limited production verification, which allows it to move into serial production beginning in 2026. The Ministry has included TK-4 procurement on its regulated military material list, confirming the shift from development to deployment planning. The exhibition also featured other US-supplied equipment, such as M1A2T tanks and M142 HIMARS launchers, together with domestically developed unmanned systems and armored vehicles, placing TK-4 within a broader modernization effort.

The procurement plan specifies a phased purchase of launcher pods for the TK-4, with 46 units scheduled in Taiwan's fiscal year 115 (2026) and 76 units in fiscal year 117 (2028), for a total of 122 launchers. Each launcher pod corresponds to one missile, reflecting a canisterized design different from earlier rectangular Tien Kung launchers. Ministry officials have indicated that the production cost details for TK-4 have not yet been finalized, though the program will be financed either through the regular defense budget or an additional special appropriation. By contrast, the TK-3 program was allocated NT$27.4 billion, of which NT$27.2 billion has been spent, and its production will conclude by the end of 2025, freeing capacity for TK-4. Observers note that Taiwan is attempting to keep overall defense spending close to 3 percent of GDP and has multiple overlapping programs covering aircraft, missiles, and base infrastructure. This context places TK-4 alongside major ongoing investments in both imported and indigenous systems.

The TK-4 incorporates several technical differences compared to the TK-3. It employs a two-stage solid rocket motor instead of the single-stage propulsion of its predecessor, which supports higher interception altitudes and improved flight performance. The missile canister measures 7.61 meters in length, significantly larger than the TK-3’s 5.49 meters, reflecting the increase in propulsion stages and structural modifications. The interceptor is assessed to reach speeds of approximately Mach 7 and is designed for engagement at altitudes up to 70 kilometers, compared to the TK-3’s ceiling of 45 kilometers. This performance exceeds the interception altitude of the US-made Patriot PAC-3 system, which can engage targets at altitudes up to about 24 km. Program information also describes the TK-4 as employing a Ka-band seeker and a domestically developed microwave power amplifier, elements that confirm it as a distinct missile rather than an extended TK-3 variant. Design similarities to Israel’s Arrow-2 and radar systems resembling Israel’s Green Pine or the US AN/TPY-2 have been noted by local media, underlining the system’s emphasis on higher-tier missile defense.

Testing and trial reports provide additional detail about TK-4’s development. In August 2023, Taiwan confirmed that an active phased-array radar developed under the Strong Bow program had been successfully integrated with the TK-3 system, though the TK-4 interceptor was not yet available at that time. In September 2025, NCSIST released multiple live-fire notifications covering tests between September 23 and October 2 at Jiupeng Range on Taiwan’s east coast, including one missile launch reaching an altitude of about 30.5 kilometers. Local media attributed these trials to the TK-4 program, suggesting the interceptor had entered live testing. Footage presented during TADTE 2025 showed the TK-4 radar tracking targets and missiles being fired from mobile launchers. The missile body displayed a tapered front with a wider rear stage, consistent with a two-stage propulsion system, and launch canisters were cylindrical, a departure from the rectangular design of earlier Tien Kung variants. These developments confirm the system has moved from design toward operational testing in preparation for mass production.

The TK-4 builds on decades of development in Taiwan’s Tien Kung missile family. TK-1, completed in 1986, introduced the domestically developed Chang Bai phased-array radar and gave Taiwan its first indigenous long-range air defense system, initially with semi-active radar homing. TK-2, introduced in 1997, added an active radar seeker and improved range, using modified box launchers and upgraded radars. TK-3 entered production in 2014, using a Ku-band active radar seeker, improved mobility, and an integrated battle management system designed to intercept tactical ballistic missiles. By 2019, production was accelerated under government orders in response to regional missile threats, and the Ministry announced in 2023 the construction of twelve bases for TK-3, half scheduled for completion by the end of 2025 and the rest by 2026. These progressive steps show how TK-4 fits into a sequence of incremental increases in altitude, mobility, and radar sophistication within the Tien Kung series.

In addition to TK-4, the Strong Bow program includes further derivative concepts. Strong Bow II has been described in two sub-variants: the IIA missile is expected to intercept at altitudes of about 100 kilometers, placing it in the same category as the US THAAD system, while the IIB missile has been reported as a surface-to-surface ballistic missile with a possible range of up to 1,000 kilometers. Separate reports have also referenced a TK-5 research path that would formalize the 100-kilometer interception capability as the next step in indigenous development. These projects remain in early stages but are included in Ministry planning documents and could be submitted for formal evaluation in the coming years. The Strong Bow family, therefore, represents both an immediate fielding of TK-4 in the mid-2020s and a longer-term plan to extend Taiwan’s missile defense and strike options.

Written by Jérôme Brahy

Jérôme Brahy is a defense analyst and documentalist at Army Recognition. He specializes in naval modernization, aviation, drones, armored vehicles, and artillery, with a focus on strategic developments in the United States, China, Russia, Türkiye, and Belgium. His analyses go beyond the facts, providing context, identifying key actors, and explaining why defense news matters on a global scale.