Based on the visual features of the stamps and envelopes provided, here are the details regarding their origins and history:

Envelope Analysis

Air Mail Markings: A blue label with "BY AIR MAIL" and its Greek equivalent "ΑΕΡΟΠΟΡΙΚΩΣ".

Addressee: It is addressed to Dr. Croutiris at 30 E Main St, Mount Kisco, N.Y., U.S.A.. from 401 Military Hospital in Athens

Stamp Details

The back of the envelope features a block of six green Greek stamps, each with a denomination of 250 drachmas. An additional orange/brown stamp with a higher denomination is placed separately on the right.

Green Stamps (Multiple): These 250 Drachmae stamps depict the Battle of Pindus (1946) during the Greco-Italian War. They show women carrying supplies over mountains, a common theme in Greek philately commemorating WWII.

Overprints: The top envelope includes a 50 Drachmae stamp with a surcharge, often used during periods of high inflation or postal rate changes.