Mayang Island is the site of a large submarine base that has both production and repair facilities. Surface-to-ship missiles had already been deployed to the site by the 1970s, and during the 1980s, North Korea began construction of tunnels for the missiles. North Korean defector Im Yŏng Sŏn heard that "Russian missiles were deployed here first." North Korea first received SS-N-2 Styx anti-ship missiles from the Soviet Union in 1967 or 1968, and could have been deployed here after that. Silkworm anti-ship missiles are probably deployed here now.

Sources:
[1] Interview with North Korean defector Im Yŏng Sŏn by Daniel A. Pinkston, senior research associate, Center for Nonproliferation Studies, 14 December 2001, Seoul;
[2] Federation of American Scientists, "North Korea Special Weapons Guide," www.fas.org;
[3] Eya Osamu, Seimitsu: Sekaikikenchizu; Hanransuru Kitachosen (Tokyo: Tokuma Shoten, 1995), p. 232;
[4] Lee Mi Suk, "Pukhan Missile Chejogonjang Ch'oeso 4 Kot Unyŏng," Munhwa Ilbo, 25 March 1999, in KINDS, www.kinds.or.kr;
[5] Chang Chun Ik, Pukhan Haek-Missile Chŏnjaeng (Seoul: Sŏmundang, May 1999);
[6] Joseph S. Bermudez, Jr., "A History of Ballistic Missile Development in the DPRK," Occasional Paper No. 2, Center for Nonproliferation Studies, November 1999;
[7] Joseph S. Bermudez, Jr., The Armed Forces of North Korea (New York: I.B. Tauris, 2001).