In Zen at War, Daizen, an ordained Soto Zen priest, documented that in the Japanese Buddhist establishment of the 1930s and 1940s there was strong support, especially in Zen, for Japanese warmaking. He traced the old connections between Zen and Samurai warrior culture in feudal Japan. Daizen also provided quotes from 19th and 20th century Zen monks and teachers that seem to say Zen approves of the slaughter of war.
For example, a prominent and revered master, Sawaki Kodo (1880-1965), is portrayed as an enthusiastic war proponent. Master Sakaki, who served as a soldier in the Russian-Japanese War of 1904-1995, is quoted as saying he and his fellow soldiers "gorged ourselves on killing people." Please note, however, that some scholars are stepping forward to say Sawaki Kodo was misquoted, and I'll come back to this in a minute.
When Zen at War was first published in 1997, American Zen teachers openly acknowledged it, talked about it, and encouraged students to read it. This was true even of teachers who were lineage holders of some of the Japanese masters portrayed as pro-war. I didn't see anyone try to excuse or sugar-coat Daizen's portrayal of Japanese Zen.
Nobody ever tried to deny this stuff in my experience. Now I've read the criticisms by Warner and Cohen, and I think they've got a point, too especially given my reading of the Japanese text in question, but the reality is, this stuff is bound up in the militarist cultural history of Japan, rightly or wrongly.
Eventually though, what we do is influenced by those who came before, and intimately permeated by it, but it is we who still sign on the dotted line.