William Laird Clowes, The Royal Navy: A History from the Earliest Times to the Death of Queen Victoria (Sampson Low, Marston and Company, 1901), vol. 6, pp. 279-304. (complete view on Google Books)
This is a partisan, patriotic account—but very useful on the battles as they unfolded. Some of the military information in this Visualizing Cultures unit derives from this source.

Hosea Ballou Morse, The International Relations of the Chinese Empire (Longmans, Green, and Co., London, NY, Bombay, Calcutta, 1910), vol. 1, The Period of Conflict, 1834-1860, chapters 1 through 13.
(complete view on Google Books)

Hsin-pao Chang, Commissioner Lin and the Opium War (Harvard University Press, 1964). (preview)

W. Travis Hanes and Frank Sanello, The Opium Wars: The Addiction of One Empire and the Corruption of Another (Sourcebooks, Inc., 2002). (preview)

Frederic E. Wakeman’s often cited analysis of the Sanyuanli incident in his book Strangers at the Gate: Social Disorder in South China, 1839-1861. (view)

Susanna Hoe, Derek Roebuck, The Taking of Hong Kong: Charles and Clara Elliot in China Waters (Hong Kong University Press, 1999, 2009). (preview)

Korea in the Eye of the Tiger at the Korean History Project website at
https://www.loc.gov/item/2003618491
Chapters 17, 18, and 19 of this unannotated narrative account address the first
Opium War in a readable way that may be particularly appealing to teachers and students.

The following sources are not online, but provide solid textbook accounts of the first Opium War:

Immanuel C. Y. Hsü, The Rise of Modern China (Oxford University Press, 1970),
ch. 8

Jonathan Spence, The Search for Modern China (Norton, 1999), pp. 147-64.

Jonathan Spence, “Opium,” Chinese Roundabout (Norton, 2003), pp. 228-56, 372-82.

John K. Fairbank, Edwin O. Reischauer & Albert M. Craig, East Asia: Tradition and Transformation (Houghton Mifflin, 1978), pp. 448-61.

The following monographs address various aspects of the first Opium War in detail:

Peter Ward Fay, The Opium War, 1840-1842: Barbarians in the Celestial Empire (University of North Carolina Press, 1998)

Arthur Waley, The Opium War through Chinese Eyes (Stanford University Press, 1963)

Jessie Gregory Lutz, Opening China: Karl F. A. Gützlaff and Sino-Western Relations, 1827-1852 (William B. Erdsman Publishing, 2008)

Jack Beeching, The Chinese Opium Wars (Harcourt Brace Jovanovich, NY and London, 1975)

A number of sites on Wikipedia provide useful information about the first Opium War, along with graphics and helpful crosslinks. The topical list that follows here focuses on battles, is roughly chronological, and is not exhaustive. Wikipedia also contains entries on individuals involved in the first Opium War (Lin Zexu, Charles Elliot et al.), as well as a (very disorderly) assemblage of images accessible through the “Images” click-on or through Wikimedia.

“First Opium War”
“Battles of the First Opium War”
“Battle of Kowloon”
“Battle of Chuenpee”
“Capture of Chusan”
“Battle of the Barrier”
“Second Battle of Chuenpee”
“Convention of Chuenpee”
“Battle of the Bogue”
“Battle of First Bar”
“Battle of Whampoa”
“Battle of Canton”
“Battle of Chinkiang”

Excerpts from Blair B. Kling, “Partner in Empire: Dwarkanath Tagore and the age of enterprise in eastern India,” (University of California Press, Berkeley and Los Angeles, London, 1976), esp. a description of the Waterwitch, 90-1. (view)

Article from Abel Stevens, editor, “The National Magazine, devoted to Literature, Art, and Religion, Volume 5, July to December, 1854,” (Carlton & Phillips, NY, 1854), esp. “The Opium Trade in the East,” 335-41. (view)

1882 publication The Truth about Opium Smoking, which reproduces Sherwill’s Patna graphics on pages 112-17. (view)

Julia Corner, China: Pictorial, Descriptive, and Historical (Henry G. Bohn, London, 1853), esp. “Reduction of Amoy” 251-2. (view)

Excerpts from Hunt Janin, “The India-China Opium Trade in the Nineteenth Century,” (McFarland & Company, Jefferson, NC, 1999) esp. “Chinese Ships: ‘Centipedes’ and Government War Junks,” 94-5. (view)

Excerpts from “Wrecks on the New South Wales Coast,” Jack Kenneth Loney, (Lonestone Press, 1993 and 2001, Victoria, Australia), esp. “Ly-ee-moon,” 88. (view)

Karl Friedrich August Gützlaff, A Sketch of Chinese History: Ancient and Modern (John P. Haven, New York, 1834). (view) Alternate online version (view)

Excerpts from Jessie Gregory Lutz, “Opening China: Karl F.A. Gützlaff and Sino-Western relations, 1827-1852,” (Wm. B. Eerdmans, Grand Rapids, Michigan/Cambridge, U.K., 2008), esp: “Gützlaff’s Coastal Journeys: Opium Ships,” “Gützlaff and the Prosecution of the Opium War, 1840-1842.” (view)

“The Chinese Emperor, Mien-Ning,” The Illustrated Magazine of Art, vol. 1 (New York, 1853), 271-72. (view)

Excerpts from James M. Polachek, The Inner Opium War (Council on East Asian Studies, Harvard, 1992), esp. “Lin Tse-Hsu and the Anti-Opium Campaign,” 141. (view)

Yangwen Zheng, The Social Life of Opium in China, (Cambridge University Press, 2005), esp. map: “The Opium Trade in China, 1833-1839,” 71. (view)

Ssu-yu Teng & John K. Fairbank, China’s Response to the West (Harvard College, 1954, 1979, 1982), esp. “Commissioner Lin’s Program for Meeting the British Aggression.” (view)

A discussion of the parliamentary debates in W. Travis Hanes and Frank Sanello, The Opium Wars: The Addiction of One Empire and the Corruption of Another (Sourcebooks, Napier, IL, 1992). (view)