Locomotive Boiler — Correct Classification by Construction and Service Identify the correct description of a locomotive boiler from the options below.

Introduction:
Locomotive boilers powered rail transport for decades and remain classic examples in boiler textbooks. Knowing their construction features helps distinguish them from stationary plant units and clarifies why they were effective in mobile service.

Given Data / Assumptions:

• Fire-tube design with numerous small-diameter tubes (multitubular).
• Horizontal orientation to fit locomotive frames.
• Internal firebox (internally fired) within the boiler shell.
• Mobile application mounted on locomotive chassis.

Concept / Approach:
A locomotive boiler is a horizontal, multitubular, internally fired, mobile fire-tube boiler. The many tubes provide large heating surface per unit length, while the internal firebox allows compact integration with the engine and draft control via blastpipe and chimney.

Step-by-Step Solution:
Check tube arrangement: many small tubes ⇒ multitubular.Check firing: firebox inside the shell ⇒ internally fired.Check service: locomotive ⇒ mobile.Therefore, option C matches all attributes.

Verification / Alternative check:
Historical locomotive boiler diagrams confirm the internal firebox, tube nest, and compact horizontal layout optimized for mobile steam generation.

Why Other Options Are Wrong:

• Single-tube or vertical: incorrect for locomotive boilers.
• Externally fired/stationary: do not describe locomotives.

Common Pitfalls:
Confusing marine scotch boilers (also fire-tube) with locomotive types; the latter are specifically mobile with distinct draughting arrangements.

Final Answer:
multitubular, horizontal, internally fired and mobile boiler