This is taken from a recruiting website.
quote
An officer appointed by warrant by the Secretary of the Army, based upon a sound level of technical and tactical competence. The warrant officer is the highly specialized expert and trainer who, by gaining progressive levels of expertise and leadership, operates, maintains, administers, and manages the Army’s equipment, support activities, or technical systems for an entire career.
(Para 1-7 DA Pamphlet 600-11)
Further clarification of the role of a warrant officer is found in FM 22-100.
"Warrant officers are highly specialized, single-track specialty officers who receive their authority from the Secretary of the Army upon their initial appointment. However, Title 10 USC authorizes the commissioning of warrant officers (WO1) upon promotion to chief warrant officer (CW2). These commissioned warrant officers are direct representatives of the president of the United States. They derive their authority from the same source as commissioned officers but remain specialists, in contrast to commissioned officers, who are generalists. Warrant officers can and do command detachments, units, activities, and vessels as well as lead, coach, train, and counsel subordinates. As leaders and technical experts, they provide valuable skills, guidance, and expertise to commanders and organizations in their particular field."
(Para A-3, Field Manual 22-100)
end quote
hope this helps.