Sun retreated to Jinan by railway on 17–18 April, leaving the path to Jinan open to the NRA.[14] When the Japanese learned of Sun's failure to defend Shandong, Prime Minister Tanaka, on the counsel of his military advisors, decided to deploy the 6th Division to Jinan on 19 April, in what was called the "Second Shandong Expedition" (第二山東出兵, Dai-ni Santō Shuppei).[14][15] Whilst Tanaka had misgivings about whether it was prudent to launch the expedition, his party, the Rikken Seiyūkai, had run on a platform of "protecting nationals on the spot" in the February 1928 election, limiting his ability to moderate the Japanese response.[16] Even before Tanaka had given the order, troops under the command of General Fukuda Hikosuke had begun arriving in Jinan via the Qingdao–Jinan railway, possibly as early as 10 April.[14] This was the first serious case of unilateral action by the post-Meiji Restoration Japanese military.[17] The first substantial group of 475 troops, however, arrived in Jinan from Qingdao on 20 April.