Many of the early KMT/ROC founders were very pro-German. Dr. Sun himself was impressed at German's social welfare program (Germany was the first EU nation to have national social security, health care, disability insurance, etc).
During the brief period of Gemran military assistance to China, they trained 400,000 to 600,000 (numbers disputed) infantry and helped the ROC to establish its first armored force. Besides the funny stormtrooper helmets, the ROC military also imported items such as the German 88mm dual-use guns, and acquired local manufacturing rights to make copies of some German small arms.
The first battle that the German-trained divisions were committed to was the Battle of Shanghai. Historians would later fault Chiang for sending his troops into a hopeless situation instead of retreating, but Chiang wanted to show the world that his troops could indeed fight the Japanese. So he ordered the 8th, 9th, 14th, 15th, 17th, & 19th group armies to defend Shanghai at any cost.
The total number of nationalist armed forces committed to Shanghai has been estimated at anywhere from 400,000 to 600,000+. Because the defenders included not only regular central army units, but also local divisions and "peace and preservation corps" plus volunteers, the numbers are quite muddled. They managed to hold off the Japanese for 3 months at the cost of 100,000 to 200,000 casualties. The Japanese lost 60,000 to 70,000 casualties.