The two Kims visited factories manufacturing steel, tire, tractors, and other machinery equipment in Jagang Province where the munitions industry is concentrated, according to the North's media reports and sources in Seoul.
Kim Jong-Il urged officials and workers there to make all-out efforts to accomplish his father's and the country's founding leader Kim Il-Sung's dream of building a "kangsong taeguk" (strong and prosperous state), the Korean Central News Agency reported.
Kim Jong-Il has long promised to "open the gate to a kangsong taeguk" in 2012 when the country marks the 100th birthday of Kim Il-Sung, and the 70th birthday of Kim Jong-Il, who is expected to formally annoint Jong-Un as his successor for a third generation of family rule.
During his visit to Jagang Province, Kim Jong-Il also praised company officials for equipping factories with computer numeric control (CNC), a production system allegedly invented and developed by Kim Jong-Un, the KCNA report said.
Jagang Province has been described as the home of CNC technology. The North's media has said output of many factories jumped on the back of the CNC mechanism, which has been dubbed as Jong-Un's primary achievement.
Almost everything — from plastic pencils to the ubiquitous vinalon — is now made "on a CNC basis," according to state publications.
Officials and analysts in Seoul consider the senior Kim's praise of CNC as part of efforts to identify the achievement of his son and heir.
North Korea's newspapers that never use English letters frequently print "CNC," a clear sign that the technology is being used to boost Jong-Un's leadership, according to Cheong Seong-Chang, a senior analyst at the private Sejong Institute think tank in Seoul.