Question:  John Luke Porter began working for the Confederate States Navy at the oldest and largest industrial facility that belongs to who?

Context paragraphs:
Cryogenic oxygen plant: A cryogenic oxygen plant is an industrial facility that creates molecular oxygen at relatively high purity.  Oxygen is the most common element in the earth's crust and the second largest industrial gas.  This process was pioneered by Dr. Carl von Linde in 1902.

John L. Porter: John Luke Porter (1813 – December 14, 1893), whose father was a shipwright at Portsmouth, Virginia, was born in 1813.  He became a United States Navy civilian employee during the 1840s and a Naval Constructor in 1859.  After resigning from the U.S. Navy in May 1861, he began working for the Confederate States Navy at the Gosport (Norfolk) Navy Yard, at Portsmouth.  He played an important role in the conversion of the scuttled and burned steam frigate USS "Merrimack" to an ironclad, which became CSS "Virginia" when commissioned in February 1862.

Confederate States Naval Academy: The Confederate States Naval Academy was an undergraduate academy in Richmond, Virginia of the Confederate States of America that educated and commissioned officers of the Confederate States Navy.  The CS Naval Academy was established by an act of the Congress of the Confederate States on April 21, 1862 and graduated a number of midshipmen before being disbanded on May 2, 1865 in Abbeville, South Carolina subsequent to the fall of the Confederate States.

Confederate States War Department: The Confederate States War Department was a cabinet-level department in Confederate States of America government responsible for the administration of the affairs of the Confederate States Army.  The War Department was led by the Confederate States Secretary of War.  During its existence, the War Department was the largest department of the Civil Service in Confederate States of America.

Misr Spinning and Weaving Company: The Misr Spinning and Weaving Company (Arabic: شركة مصر للغزل والنسيج‎ ‎ ), also known as Misr Helwan or the El-Ghazl factory, is a large, publicly owned textile company located in El-Mahalla El-Kubra within the Nile Delta of Egypt, approximately 80 kilometers north of Cairo.  The company's current board chairman is Mohamed Moheb Salah Elden.  Egypt's largest industrial facility, Misr Helwan employs over 25,000 workers, many of whom have played an active role in Egyptian labor struggles.  Large protests and strikes at Misr Helwan since 2006 contributed to the collapse of the Mubarak government, the 2011 Egyptian revolution, and the Arab Spring more generally.

Military of the Confederate States of America: The Military of the Confederate States of America existed between 1861 and 1865, and was tasked throughout its existence with fighting the American Civil War.  It comprised three branches: the Confederate States Army, the Confederate States Navy and the Confederate States Marine Corps.  It was disbanded with the collapse of the Confederacy.

Confederate States Navy: The Navy of the Confederate States (CSN) was the naval branch of the Confederate States Armed Forces, established by an act of the Confederate States Congress on February 21, 1861.  It was responsible for Confederate naval operations during the American Civil War (1861-1865), fighting against the Union Navy / United States Navy.

Norfolk Naval Shipyard: The Norfolk Naval Shipyard, often called the Norfolk Navy Yard and abbreviated as NNSY, is a U.S. Navy facility in Portsmouth, Virginia, for building, remodeling, and repairing the Navy's ships.  It is the oldest and largest industrial facility that belongs to the U.S. Navy as well as the most multifaceted.  Located on the Elizabeth River, the yard is just a short distance upriver from its mouth at Hampton Roads.

Richmond in the American Civil War: Richmond, Virginia, served as the capital of the Confederate States of America for almost the whole of the American Civil War.  Not only was Richmond the seat of political power for the Confederacy, it served as a vital source of munitions, armament, weapons, supplies, and manpower for the Confederate States Army and Confederate States Navy, and as such would have been defended at all costs regardless of its political status.  The city was less than 100 mi from the Union capital in Washington, D.C..

Confederate Roll of Honor: The Confederate Roll of Honor was authorized by the Confederate Congress on October 13, 1862 as a means of honoring the valor and bravery of members of the Confederate States Army, Confederate States Navy, and Confederate States Marine Corps.

Supporting paragraphs: John L. Porter Norfolk Naval Shipyard
Answer: the U.S. Navy