From China's Chongming-Taicang Yangtze River Tunnel to projects worldwide, tunnel boring machines (TBMs) are the backbone of underground engineering feats. China has produced over 4,000 TBMs, capturing 70 percent of the global market, with China Railway Engineering Equipment Group (CREG) leading production and sales for eight consecutive years. How do these steel giants operate, and what drives their global success? Let's dive in.