Cyrus B . Comstock Cyrus Ballou Comstock ( February 3 , 1831 – May 29 , 1910 ) was a career officer in the Regular Army of the United States . After graduating from the United States Military Academy at West Point in 1855 , Comstock served with the Army Corps of Engineers . At the beginning of the American Civil War , he assisted with the fortification of Washington , D . C . In 1862 , he was transferred to the field , eventually becoming chief engineer of the Army of the Potomac . In 1863 during the Siege of Vicksburg , he served as the chief engineer of the Army of the Tennessee . The most significant phase of Comstock ' s career began in November 1864 when he was appointed to the staff of Lt . Gen . Ulysses S . Grant , becoming Grant ' s senior aide - de - camp . In 1865 , Comstock was appointed the senior engineer in the assault on Fort Fisher , North Carolina , and the assault on Mobile , Alabama , both of which were successful . By the end of the war , Comstock had earned the awards of the honorary grades of brevet major general in the Volunteer Army and brevet brigadier general in the Regular Army . After the close of the war , Comstock served on the military commission for the trial of the conspirators in the assassination of President Abraham Lincoln . He was dismissed from the commission for his criticism of the proceedings . Later Comstock continued with the Army Corps of Engineers , took part in several engineering projects , and served on the Mississippi River Commission , of which he was president . Early life . Born in Wrentham , Massachusetts , to Nathan and Betsy Comstock on February 3 , 1831 , Cyrus Comstock attended the United States Military Academy at West Point . He graduated first in his class in 1855 . Following his graduation , Comstock was assigned to the Army Corps of Engineers and assisted with the design and construction of several fortifications . He also served as an instructor of engineering at West Point . Civil War service . At the commencement of the Civil War , Comstock , then holding the rank of first lieutenant in the Regular Army , was transferred from West Point to Washington , D . C . He became an assistant to Brig . Gen . John G . Barnard , the engineer in charge of the fortifications of Washington and later chief engineer of the Army of the Potomac . Army of the Potomac . When the Army of the Potomac took the field in the spring of 1862 during Maj . Gen . George B . McClellan ' s Peninsular Campaign , Comstock continued to serve as Barnard ' s assistant . On June 1 , 1862 , during the Peninsular Campaign , Comstock was appointed chief engineer of the II Corps . He continued with the Army of the Potomac through the remainder of the Peninsular Campaign and through the Maryland Campaign . Maj . Gen . Ambrose Burnside succeeded McClellan and appointed Comstock the chief engineer of the Army of the Potomac . During the Fredericksburg Campaign , Comstock was faced with the difficult task of constructing pontoon bridges over the Rappahannock River , a debacle which proved to be one of the most challenging of his career . Due to confusion in Washington , D . C . at the War Department , the materials necessary for the construction of the bridges did not arrive at Falmouth , Virginia at the same time as the Army of the Potomac . Despite Comstock ' s urgent telegraphs and messages , which went unanswered , it took nearly a month for the pontoons to arrive during which time the Union army had completely lost the element of surprise , the Confederate army had dug in at Fredericksburg , Virginia and morale within the Army of the Potomac had sunk . When the material for the bridges finally did arrive , Comstock personally led men from the 50th New York Engineers in seeing to the task of construction . In piecing together the bridges on the Rappahannock River , Comstock and other soldiers were dangerously exposed to enemy fire . When Maj . Gen . Joseph Hooker reorganized the Army of the Potomac in the spring of 1863 , Comstock was removed as chief engineer of that army and placed in command of a battalion of engineers . In that capacity , he played an important role in the Battle of Chancellorsville , overseeing the construction of pontoon bridges over various rivers which first allowed the advance of the Army of the Potomac and later facilitated its retreat after Union forces were defeated . Siege of Vicksburg . After the Battle of Chancellorsville , Comstock was transferred to the Army of the Tennessee which was , at that time , involved in the Siege of Vicksburg , Mississippi , under the command of Maj . Gen . Ulysses Grant . Comstock arrived at Vicksburg in June 1863 and set to work on improving the siege works . His efforts earned Grant ' s respect . Comstock was soon promoted to major and appointed chief engineer of the Army of the Tennessee . The Siege of Vicksburg was successful , in part due to Comstock ' s supervision of the overall siege works , and the city surrendered to Union forces on July 4 , 1863 . This victory marked a major turning point in the war as the Union Army gained control of the Mississippi River . The impression that Comstock made on Grant would have a significant impact on Comstock ' s career later in the war . Comstock remained with the Army of the Tennessee into the fall of 1863 . On November 19 , he became assistant inspector general of the Department of the Mississippi and promoted to lieutenant colonel of volunteers . He served in this role until March 1864 . General Grant ' s staff . On March 12 , 1864 , Grant was appointed general - in - chief of the United States Army and moved his headquarters to the eastern theater in Virginia . Grant asked Comstock to come with him as his senior aide - de - camp . Grant determined to command in the field , following and directing the movements of the Army of the Potomac in a major offensive during the summer of 1864 known as the Overland Campaign . During the campaign , Comstock played a key role in coordinating the movements of the various corps of the army and personally conveying Grant ' s orders to the corps commanders . His efforts were particularly successful during the Battle of the Wilderness for which Comstock won a commendation from Grant and a brevet promotion to lieutenant colonel in the Regular Army . Comstock was temporarily detached from Grant ' s staff and appointed by Grant to the post of chief engineer of the Department of North Carolina in January 1865 . The transfer was prompted by Maj . Gen . Benjamin Butler ' s failure to take Fort Fisher in December 1864 . The fort was the last Confederate stronghold on the east coast . Serving under the command of Maj . Gen . Alfred Terry , Comstock assisted in planning a second and successful assault on Fort Fisher . Following this victory , Comstock was awarded the grade of brevet colonel in the Regular Army . Comstock also was nominated by President Abraham Lincoln on January 23 , 1865 for the award of the honorary grade of brevet brigadier general , U . S . Volunteers , to rank from January 15 , 1865 , for gallant services in the capture of Fort Fisher and the U . S . Senate confirmed the award on February 14 , 1865 . He returned to Virginia and to his role as Grant ' s senior aide , but did not remain long . In March 1865 , Grant again dispatched Comstock to aid in a key siege operation — this time to Mobile , Alabama , the last Confederate stronghold on the Gulf of Mexico . There Comstock served under Maj . Gen . Edward Canby and assisted in operations leading to the surrender of Mobile after the Battle of Spanish Fort and the Battle of Fort Blakely in April 1865 . While Comstock was serving in Alabama , Gen . Robert E . Lee surrendered to Grant after the Battle of Appomattox Courthouse , essentially ending the Civil War . On January 13 , 1866 , President Andrew Johnson nominated Comstock for the award of the honorary grade of brevet major general , U . S . Volunteers , to rank from March 26 , 1865 , for faithful and meritorious services during the campaign against the city of Mobile and its defenses , and the U . S . Senate confirmed the award on March 12 , 1866 . On April 10 , 1866 , President Andrew Johnson nominated Comstock for the award of the honorary grade of brevet brigadier general , U . S . Army , ( Regular Army ) , to rank from March 13 , 1865 , for gallant and meritorious services in the campaign ending with the capture of Mobile , Alabama , and the U . S . Senate confirmed the award on May 4 , 1866 . Post - war life . Lincoln assassination . In May 1865 , while still serving on Grant ' s staff , Comstock was called to serve as one of the nine military commissioners to oversee the trial of the conspirators in the assassination of Abraham Lincoln . At first , Comstock was eager to see the prosecution of the conspirators , writing that , for them , " death is too good . " However , as the trial proceeded , Comstock became disturbed by the secrecy of the military proceedings . Concerned about the violation of the defendants ' rights , he began to openly argue for the case to be transferred to a civilian court . President Andrew Johnson removed Comstock from the commission due to Comstock ' s protests . The rationale for the removal , as explained to Comstock by Secretary of War Edwin M . Stanton , was that Grant had also been a potential target of the conspirators and the commissioners felt that Comstock , due to his closeness to Grant , could not be counted on to act impartially . Later career . Comstock served on Grant ' s staff until 1866 , then returned to service with the Corps of Engineers and remained on active duty until 1895 when he retired with the rank of colonel . In the course of his post - war duty , he served with several boards and commissions including the Permanent Board of Engineers in New York City , the geodetic survey of the north and northwestern lakes of the United States , and was president for many years of the Mississippi River Commission . Comstock was a prominent member of the National Academy of Sciences and bequeathed a fund to the Academy to support an award to a scientist conducting innovative work in the investigation of electricity , magnetism , or radiant energy . Today known as the Comstock Prize in Physics , the award in the amount of $ 20 , 000 is granted every five years by the Academy . Family . In 1869 , Comstock married Elizabeth Blair , daughter of Montgomery Blair who had served as United States Postmaster General during the Lincoln administration . They had a daughter , Elizabeth Marion Comstock , who was born in Detroit , Michigan in 1872 while Comstock was at work on the geodetic survey of the Great Lakes .