Dressed in military camouflage with an assault rifle at the ready, "Prof" Yeh peers from behind a vehicle in a parking lot outside Taipei, scanning his surroundings and waiting for a signal to advance.
Yeh actually works in marketing, and his weapon is a replica -- but he is spending the weekend attending an urban warfare workshop, to prepare for what he sees as the very real threat of a Chinese invasion.
When Russian President Vladimir Putin ordered his troops to invade Ukraine at the end of February, he gave shape to the darkest fears of many Taiwanese.
The self-governed democracy lives under constant threat from authoritarian China, which views the island as part of its territory and has pledged to take it one day.
But the war in Ukraine has also inspired Yeh.
The resilience of Ukrainian forces has given him hope that with the right tactics, Taiwan too might have a chance defending itself against its much mightier neighbour.