Since FamilySearch's catalog description was written, the US National Archives (NARA) has replaced the OPA system with the new Catalog. What you want for this purpose are the electronic passenger list databases, which are at NARA's AAD (Access to Archival Databases) website.
From the AAD home page, look for where it says "Browse by Category" and then "Genealogy/Personal History", then choose Passenger Lists.
You want the data described as Data Files Relating to the Immigration of Germans to the United States, created, ca. 1977 - 2002, documenting the period 1850 - 1897, which consists of two files:
Searching on AAD requires the user to search the passenger data file first. Search results look like this:
Click the document icon (View Record) to see details:
After getting the main search results, take the manifest number and search the Manifest Data file. The detail page for infant Max's manifest looks like this:
NARA's FAQ for the series tells us that this manifest number is part of the series of New York arrivals. Once you have the ship name and arrival port and date, search for the images on any website that offers you access to the images to get the corresponding manifest. See Joe Beine's guide on German Roots (link in the Resource Lists at the bottom of the answer) to find where you can view the images for each port.
Searching on the One-Step Web Pages
Another option, which allows the researcher to search both AAD and other sites where you can locate passenger manifest data, is available on Stephen P. Morse's One-Step Web Pages. To search AAD, choose the page:
Germans to America (1850-1897): Searching the NARA Archival Germans to the US Database in One Step
A typical search result from AAD's passenger list is displayed like this:
Clicking the link for "Get Transit" pops up a window (example using Chrome browser) with the information on the passenger's transit and destination:
Clicking the link for "Get Ship" gives you the manifest number and ship information, saving you a separate search in the Manfest Header Data file at AAD.
From the Germans to America One-Step page, you can push the button My Other Databases to return to the One-Step Web pages home page and use the passenger list tools to search for the actual manifest. Morse's tools offer choices to search several ports and search both free and paid databases. You will need an Ancestry subscription to see the images on Ancestry, or (for New York arrivals) an Statue of Liberty/Ellis Island Foundation website login to see images there. (Note: the Ellis Island website now includes the infomration for the Castle Garden period as well. Pay attention to the arrival date, and use the Gold Form or White Form or All New York Arrivals form as needed. See the Overview: Which One-Step Ellis Island Search Form Should I Use? for more information.)
As luck would have it, when I searched for my passenger using the One-Step Web Pages, I couldn't find the manifest for the General Werder, so I looked directly on Ancestry. The infant Max Bretschneider's arrival is in the New York, Passenger and Crew Lists (including Castle Garden and Ellis Island), 1820-1957. (Sometimes changing websites and starting over saves us from negative search results caused by fumble-fingered errors.)
No matter which site you use to search for the manifests, I recommend looking at the Technical Information and FAQ at the AAD website to learn more about the Scope and Content of the records, and the FAQs for any One-Step Web Page you use, and to learn more about Germans to America in general so you understand the limits of the project (see the link at the bottom of the answer for a related question).
To learn more (including how to get copies of the records) see:
- Frequently Asked Questions (FAQ) Collection CIR
Series: Data Files Relating to the Immigration of Germans to the United States PDF Download especially the answer to How do these records relate to the published Germans to America series?
- information for the series, including Scope and Content (if the link doesn't work, look for the information link on any search or results page)
- Technical Information (includes Supplementary Notes)
Special note: if your passengers' port of embarkation was Hamburg, you can also use the ship information to look for the corresponding German list in the Hamburg Passenger Lists. (Bremen outgoing lists are only available for a few years since most lists were discarded.)
Other information about the Germans to America series (and its limitations) can be found in the related question Finding alternate indexes or record sets for passenger lists / ship manifests from Germany?