<p>ASHINGTON -- The Marine Corps relieved one of its top commanders in Iraq yesterday, an extremely unusual action, especially for a unit engaged in combat.</p>
<p>Colonel Joe W. Dowdy has been the officer in charge of the First Marine Regiment, one of the three major Marine Corps ground units fighting toward Baghdad. His regiment is reported to have been used to pin down Republican Guard units in the city of Kut while the other two major units, the Fifth and Seventh Marines, crossed the Tigris River on Thursday and raced toward Baghdad. Those units encountered heavy ground fighting yesterday on the outskirts of the capital and had at least three M1 tanks disabled by Iraqi fire.</p>