Operation Sea Lion: How bad could it have gone?

The scale of Sea Lion preparations sits uneasily beside German commanders' doubts and landing craft that would arrive after the invasion window.

Distinguish conditional German discussions about invading Britain in 1903 from the operational planning undertaken for Sea Lion.

Follow the proposed army embarkation routes and the problem of supplying an invasion through small seaside harbors.

The advance toward Reigate would encounter defensive terrain and fortifications on London's southern approaches.

Sea Lion's nighttime waves would meet British forces with a strong interest in night fighting.

Calling the Channel a large river crossing does little to remove the amphibious demands or make Norway a reliable precedent.

Home Guard units combined limited mobility with local knowledge and veteran experience that are difficult to represent in a wargame.

The German logistical assumptions depended on reaching London within days and obtaining food as the army advanced.

Large protective minefields offered a way to compensate for German naval weakness while giving Britain time to recognize the threat.

An interpretation of Sea Lion's persistence links the planning effort to the difficulty of telling Hitler that an operation could not work.

Proposed attacks on the power grid and Lysander mustard-gas sorties exposed their own aircraft to heavy losses.

Sea Lion diverted effort from U-boats, while claims of RAF defeat still left the Royal Navy and Britain's wider resources to confront.

Reconnaissance and routine countermining made a large German mine-laying campaign difficult to hide.

The poor language skills of some agents sent to Britain raise questions about German expectations for the intelligence mission.

Italian participation after the postponement leaves more than one explanation for Germany's continued air effort against Britain.

Heavy coastal gunfire achieved limited results against shipping, while better batteries and radar arrived gradually.

Delay gave Britain more equipment, reorganized units and prepared positions, while Germany still needed enough firepower to attack them.

Converted river barges made the invasion dependent on suitable weather, while Atlantic weather patterns favored Allied forecasting.

Gathering thousands of invasion barges removed working freight vessels from inland waterways and imposed a continuing cost.

The unloading plan left unpowered barges stationary for hours, giving British artillery time to destroy them.

The transport force had to survive unloading and return across the Channel before it could bring the next wave.

Germany had useful self-propelled engineer landing boats, but only two prototypes were in service by September 1940.

Swimming and deep-wading tanks offered ways to land armor, but transport stability and the size of the available force limited their usefulness.

Later landing bridges and jetties offered useful technology but pushed a renewed invasion into conflict with Germany's Soviet campaign.

Fighting motor torpedo boats would expose submarines to disabling gunfire or consume scarce torpedoes on small targets.

The assembled barges could reveal tidal constraints, while reconnaissance and intelligence penetration offer possible explanations for British knowledge.

British defensive construction developed alongside naval bombardments and bomber attacks on the assembly points for German landing vessels.

Local resistance could buy time for regular formations to assemble and strengthen successive defensive positions.

Invasion preparations helped Britain train and mobilize forces, while home defense later supported the release of regular troops for service overseas.

Sea Lion's planning could demonstrate the invasion's limitations while supporting equipment development for a possible later attempt.

The German worst-case scenario puts the invasion barges against a concentrated Royal Navy night attack after minelaying reveals the preparations.

Submarine radio traffic and prolonged minelaying could give Britain time to gather more warships for the invasion battle.

The Luftwaffe's 1940 threat to British ships differed from the more developed anti-shipping capability it acquired in 1941.

Destroying Sea Lion's first wave would cost Germany troops and warships while removing barges and tugboats needed to move goods.

An early German launch might put troops ashore, but losses at sea and heavily defended ports would restrict their prospects.

A small German landing could damage confidence in Britain's security and draw forces away from overseas operations despite its eventual defeat.

Invasions postponed to 1941 or 1942 must account for Britain's response to continued German amphibious preparations.

The proposed likeliest result combines heavy German losses at sea with a few landings that unsettle British home-defense planning.

Stories of an invasion destroyed by fire lead into the hypothetical danger of barges exposed to burning oil while waiting offshore.

A hypothetical German acquisition of the French fleet connects invasion defense with British distrust of Vichy and Mers-el-Kebir.