Ukraine Commanders Say a Russian Invasion Would Overwhelm Them

KYIV, Ukraine — On the 30th anniversary of the founding of Ukraine’s armed forces, President Volodymyr Zelensky donned a helmet and flak jacket to tour the trenches this week and announced with great fanfare the delivery of new tanks, armored vehicles and ships to frontline units engaged in fighting Russian forces and Kremlin-backed separatists.

The weapons systems may help to maintain parity in the slow-moving war of attrition that has prevailed for years. But neither they nor anything else the Ukrainian military can now muster would be sufficient to repel...