Here’s a news clip from 1949 on the Jehovah's Witnesses meeting that took place in New York over 8 days with 75,000 members from across America and many foreign countries in attendance. As the narrator states, so many people showed up that meetings took place in the Brooklyn Stadium and in tents on the outskirts of NYC. 

Begins with shots of crowded New York sidewalks where Jehovah’s Witnesses are waiting in the rain under umbrellas to get into a religious ceremony. Many people who are standing in line are wet and soggy yet appear positive. And many are milling about in the down pouring rain. 

The highlight of the 8-day meeting is the mass baptizing that took taking place at a swimming pool in Queens, New York. People are seen being fully-submerged in a pool— dunked backwards into the water and then quickly brought back up to the surface — as a part of the ceremony. Top-ranking preachers are officiating the many baptisms that are taking place.