New strategic accords between the U.S. and South Korea, focusing on plans to destroy North Korean nuclear missiles on the ground before they can be fired, may have influenced South Korea's decision to abandon the F-15 for the F-35.

South Korea's military planning emphasizes the development of a “kill chain” capable of destroying both fixed, hardened targets and mobile weapons such as transporter-erector-launchers for ballistic missiles. This responds to the increasing use of such missiles by the North, including an eight-axle TEL—apparently of Chinese design—unveiled in 2012.

The kill chain incorporates overhead reconnaissance, by satellites and manned and unmanned aircraft, and precision weapons. One major new program is the Hyunmoo-3 cruise missile—developed in land-, ship- and submarine-launched versions by Korea's Agency for Defense Development and unveiled early this year— possibly with the aid of the German/Swedish Taurus Systems company, according to industry sources. Korea has announced its intention of acquiring the Taurus KEPD 350 missile to arm its F-15s.

The Hyunmoo-3 was shown publicly in a parade in Seoul on Oct. 1. The following day, South Korean Defense Minister Kim Kwan-jin and U.S. Defense Secretary Chuck Hagel signed a new bilateral agreement on “tailored deterrence” against North Korean nuclear threats.

This follows some intensive work in the Pentagon, and between the Pentagon and Korea, on the boundaries of a pre-emptive strategy aimed at degrading the North's nuclear strike capability to the point where missile defenses can handle surviving threats with high confidence. A central goal is to achieve the highest possible level of non-nuclear deterrence.

Since signing the new agreement, as well as turning to the F-35, South Korea has requested information on the Lockheed Martin Terminal High Altitude Area Defense ballistic missile defense system and has been identified as a sales prospect for the Global Hawk unmanned air system, according to South Korean media.

One of the key design missions of the F-35—established soon after the unsuccessful “Scud-hunting” campaign of the 1991 Gulf War—is to detect and strike mobile targets using stealth and low-probability-of-intercept radar. International orders are seen as necessary for the program to reach production rate and cost targets on time—so South Korea's order could be seen as helping advance the U.S. acquisition program and ensure early arrival of U.S. Air Force F-35s in the region.