1
general::
Phrase(s): shoulder to shoulder
Fig. side by side; with a shared purpose. • The two armies fought shoulder to shoulder against the joint enemy. • The strikers said they would stand shoulder to shoulder against the management.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
In close proximity or cooperation, as in The volunteers worked shoulder to shoulder in the effort to rescue the miners. This expression originated in the late 1500s in the military, at first signifying troops in close formation. Its figurative use dates from the late 1800s.
American Heritage Idioms