Day & Zimmermann is a privately held company in the fields of construction, engineering, staffing and ammunition manufacture, operating out of 150 locations worldwide.

Day & Zimmermann has an annual revenue of $2.5 billion, and is ranked by Forbes as one of the largest privately held companies in the United States.

[6] Later, the scope of the organization was enlarged to include a great deal of engineering and construction work in both the industrial and public-service fields.

[10] Day & Zimmermann is responsible for manufacturing much of the artillery munitions used by Israel in its ongoing invasion of Gaza.

[11][12] The American Friends Service Committee says that Merkava tanks fired M830A1 rounds in a November attack on a UN school in Gaza, and in the attack that killed Hind Rajab, and that serial numbers on shells recovered at the scene suggest that the shells were made by Day & Zimmermann subsidiary Mason & Hanger.