Usually main messages on flags are in cursive, or semi-cursive script.http://en.wikipedia.org/wiki/Semi-cursive_script
But as paulg commented most kanji on this flag is in regular script.http://en.wikipedia.org/wiki/Regular_script
In general, writing cursive script was a gentleman's skill, but many gentlemen did not have one. I cannot. Often families asked somebody with good hand to write main outstanding phrases but the man who wrote large letters on this flag had poor hand. And down-right line of 長should be written through to right, as 人 on below-right corner of this flag shows. This man stopped the line and moved the brush to opposite direction. This bad manner appears both in 武運長久 on center and 長澤正人(長沢正人 in modern Japanese simplified style) on below right. So I guess large 長澤正人(Nagasawa Masato) was the soldier's name and was written by the same man who wrote 武運長久.
Nobody with the family name 長澤 appears on this flag. So I suppose this flag was NOT from his family, or his colleague including aged, sophisticated men. His young friends prepared this casual flag and wrote all messages on it.
I cannot read the stamp.